diff -r 814095fc3091 src/cl_main.cpp
--- a/src/cl_main.cpp	Sun Sep 15 23:42:35 2013 +0300
+++ b/src/cl_main.cpp	Mon Sep 23 22:43:35 2013 +0300
@@ -48,6 +48,8 @@
 //
 //-----------------------------------------------------------------------------
 
+#include <map>
+#include <functional> 
 #include "networkheaders.h"
 #include "a_action.h"
 #include "a_sharedglobal.h"
@@ -1335,6 +1337,17 @@
 }
 
 //*****************************************************************************
+// [Dusk] Helper functor, this lets me use FStrings in a std::map even though
+// FString does not have operator== overloaded.
+struct client_compareStrings : std::binary_function<FString, FString, bool>
+{
+	bool operator( )( const FString& a, const FString& b )
+	{
+		return a.Compare( b ) < 0;
+	}
+};
+
+//*****************************************************************************
 //
 void CLIENT_ProcessCommand( LONG lCommand, BYTESTREAM_s *pByteStream )
 {
@@ -1407,9 +1420,11 @@
 		}
 		break;
 	case SVCC_ERROR:
-		{
-			char	szErrorString[256];
-			ULONG	ulErrorCode;
+	{
+			const FString   website = TEXTCOLOR_LIGHTBLUE "http://www." DOMAIN_NAME "/" TEXTCOLOR_ORANGE;
+			const FString	errorStart = "\n" TEXTCOLOR_ORANGE "Failed to connect: ";
+			FString			errorString;
+			ULONG			ulErrorCode;
 
 			// Read in the error code.
 			ulErrorCode = NETWORK_ReadByte( pByteStream );
@@ -1419,30 +1434,25 @@
 			{
 			case NETWORK_ERRORCODE_WRONGPASSWORD:
 
-				sprintf( szErrorString, "Incorrect password." );
+				errorString = "Incorrect password.";
 				break;
 			case NETWORK_ERRORCODE_WRONGVERSION:
 
-				sprintf( szErrorString, "Failed connect. Your version is different.\nThis server is using version: %s\nPlease check http://www." DOMAIN_NAME "/ for updates.", NETWORK_ReadString( pByteStream ));
+				errorString.Format( "Your version is different.\nThis server is using version: %s\nPlease check %s for updates.",
+					NETWORK_ReadString( pByteStream ), website.GetChars());
 				break;
 			case NETWORK_ERRORCODE_WRONGPROTOCOLVERSION:
-
-				sprintf( szErrorString, "Failed connect. Your version uses outdated network code.\nPlease check http://www." DOMAIN_NAME "/ for updates." );
+				errorString.Format( "Your version uses outdated network code.\nPlease check %s for updates.", website.GetChars() );
 				break;
 			case NETWORK_ERRORCODE_BANNED:
 
 				{
-					sprintf( szErrorString, "Couldn't connect. \\cgYou have been banned from this server!\\c-" );
+					errorString = TEXTCOLOR_RED "You have been banned from the server!" TEXTCOLOR_ORANGE;
 
 					// [RC] Read the reason for this ban.
 					const char		*pszBanReason = NETWORK_ReadString( pByteStream );
-					char			szShortBanReason[128]; // Don't allow servers to overflow szErrorString.
 					if ( strlen( pszBanReason ))
-					{
-						strncpy( szShortBanReason, pszBanReason, 127 );
-						szShortBanReason[127] = 0;
-						sprintf( szErrorString, "%s\nReason for ban: %s", szErrorString, szShortBanReason );
-					}
+						errorString.AppendFormat( "\nReason for ban: %s", pszBanReason );
 
 					// [RC] Read the expiration date for this ban.
 					time_t			tExpiration = (time_t) NETWORK_ReadLong( pByteStream );
@@ -1453,53 +1463,100 @@
 
 						pTimeInfo = localtime( &tExpiration );
 						strftime( szDate, 32, "%m/%d/%Y %H:%M", pTimeInfo);
-						sprintf( szErrorString, "%s\nYour ban expires on: %s (server time)", szErrorString, szDate );
+						errorString.AppendFormat( "\nYour ban expires on: %s (server time)", szDate );
 					}
 					break;
 				}
 			case NETWORK_ERRORCODE_SERVERISFULL:
 
-				sprintf( szErrorString, "Server is full." );
+				errorString = "Server is full.";
 				break;
 			case NETWORK_ERRORCODE_AUTHENTICATIONFAILED:
 			case NETWORK_ERRORCODE_PROTECTED_LUMP_AUTHENTICATIONFAILED:
-				{
-					std::list<std::pair<FString, FString> > serverPWADs;
+			{
+					errorString.Format( "%s authentication failed.\nPlease make sure you are using the exact same WAD(s) as the server, and try again.\n\n",
+						( ulErrorCode == NETWORK_ERRORCODE_PROTECTED_LUMP_AUTHENTICATIONFAILED ) ? "Protected lump" : "Level" );
+
+					enum { Missing, Different, Matches, Extra };
+					std::list<std::pair<FString, FString> >::iterator it;
+					std::map<FString, int, client_compareStrings> wadStates;
+					FString extraWads;
+
+					// [Dusk] Server also sends the IWAD for further processing.
+					const FString iwadName = NETWORK_ReadString( pByteStream ),
+						iwadSum = NETWORK_ReadString( pByteStream );
 					const int numServerPWADs = NETWORK_ReadByte( pByteStream );
+
+					errorString.AppendFormat( TEXTCOLOR_NORMAL "IWAD: %s: %s\n", iwadName.GetChars( ),
+						( iwadSum.Compare( NETWORK_GetIWADChecksum( )) == 0) ? TEXTCOLOR_GREEN "MATCHES" : TEXTCOLOR_RED "DIFFERENT" );
+
+					if ( numServerPWADs > 0 )
+						errorString += TEXTCOLOR_NORMAL "PWADs:\n";
+
+					// [Dusk] Mark any PWADs on our end extra by default - the WADs the server does
+					// have loaded will have their state changed in the next loop.
+					for ( it = NETWORK_GetPWADList( )->begin( ); it != NETWORK_GetPWADList( )->end( ); ++it )
+						wadStates[it->first] = Extra;
+
+					// [Dusk] Go through the server's WADs and find our counterparts
 					for ( int i = 0; i < numServerPWADs; ++i )
 					{
-						std::pair<FString, FString> pwad;
-						pwad.first = NETWORK_ReadString( pByteStream );
-						pwad.second = NETWORK_ReadString( pByteStream );
-						serverPWADs.push_back ( pwad );
+						const FString pwadName = NETWORK_ReadString( pByteStream ),
+							pwadSum = NETWORK_ReadString( pByteStream );
+						int state = Missing;
+
+						// [Dusk] Compare the data and tell the relationships between pwads (matches/different/missing)
+						// The WAD is considered matched if it is found and the checksum matches, different if
+						// found but checksum is different and missing if not found at all.
+						for ( it = NETWORK_GetPWADList( )->begin( ); it != NETWORK_GetPWADList( )->end( ); ++it )
+						{
+							if ( it->first.Compare( pwadName ) == 0 )
+							{
+								state = ( it->second == pwadSum ) ? Matches : Different;
+								break;
+							}
+						}
+
+						// [Dusk] Mark this down.
+						wadStates[pwadName] = state;
 					}
 
-					sprintf( szErrorString, "%s authentication failed.\nPlease make sure you are using the exact same WAD(s) as the server, and try again.", ( ulErrorCode == NETWORK_ERRORCODE_PROTECTED_LUMP_AUTHENTICATIONFAILED ) ? "Protected lump" : "Level" );
-
-					Printf ( "The server reports %d pwad(s):\n", numServerPWADs );
-					for( std::list<std::pair<FString, FString> >::iterator i = serverPWADs.begin( ); i != serverPWADs.end( ); ++i )
-						Printf( "PWAD: %s - %s\n", i->first.GetChars(), i->second.GetChars() );
-					Printf ( "You have loaded %d pwad(s):\n", NETWORK_GetPWADList( )->size() );
-					for( std::list<std::pair<FString, FString> >::iterator i = NETWORK_GetPWADList( )->begin( ); i != NETWORK_GetPWADList( )->end( ); ++i )
-						Printf( "PWAD: %s - %s\n", i->first.GetChars(), i->second.GetChars() );
-
+					// [Dusk] Now go through the information we processed and digest it into output. We stuff
+					// the extra WAD information into a separate paragraph since the server does not have them
+					// and the first PWAD list is for the WADs the server has loaded but the client potentially
+					// does not.
+					for ( std::map<FString, int, client_compareStrings>::iterator it = wadStates.begin( ); it != wadStates.end( ); it++ )
+					{
+						if ( it->second != Extra )
+							errorString.AppendFormat( TEXTCOLOR_NORMAL "- %s: %s\n", it->first.GetChars( ),
+								( it->second == Matches ) ? TEXTCOLOR_GREEN "MATCHES" :
+								( it->second == Different ) ? TEXTCOLOR_RED "DIFFERENT" :
+								TEXTCOLOR_RED "MISSING" );
+						else
+							extraWads.AppendFormat( TEXTCOLOR_NORMAL "-" TEXTCOLOR_RED " %s\n", it->first.GetChars( ));
+					}
+
+					// [Dusk] If there were any extraneous WADs, append that information to the error.
+					if ( extraWads.IsNotEmpty( ))
+						errorString.AppendFormat( TEXTCOLOR_ORANGE "\nYou have these WADs loaded the server does not:\n%s",
+							extraWads.GetChars( ));
 					break;
 				}
 			case NETWORK_ERRORCODE_FAILEDTOSENDUSERINFO:
 
-				sprintf( szErrorString, "Failed to send userinfo." );
+				errorString = "Failed to send userinfo to the server.";
 				break;
 			case NETWORK_ERRORCODE_TOOMANYCONNECTIONSFROMIP:
 
-				sprintf( szErrorString, "Too many connections from your IP." );
+				errorString = "The server has too many connections from your IP.";
 				break;
 			default:
 
-				sprintf( szErrorString, "Unknown error code: %d!\n\nYour version may be different. Please check http://www." DOMAIN_NAME "/ for updates.", static_cast<unsigned int> (ulErrorCode) );
+				errorString.Format( "Unknown error code recieved: %lu\nYour version may be different. Please check http://www." DOMAIN_NAME "/ for updates.", ulErrorCode );
 				break;
 			}
 
-			CLIENT_QuitNetworkGame( szErrorString );
+			CLIENT_QuitNetworkGame(( errorStart + errorString ).GetChars( ));
 		}
 		return;
 	case SVC_HEADER:
diff -r 814095fc3091 src/network.cpp
--- a/src/network.cpp	Sun Sep 15 23:42:35 2013 +0300
+++ b/src/network.cpp	Mon Sep 23 22:43:35 2013 +0300
@@ -106,6 +106,7 @@
 
 static	std::list<std::pair<FString, FString> >	g_PWADs;
 static	FString		g_IWAD; // [RC/BB] Which IWAD are we using?
+static	FString		g_IWADChecksum; // [Dusk] MD5 checksum of the IWAD
 
 FString g_lumpsAuthenticationChecksum;
 FString g_MapCollectionChecksum;
@@ -904,6 +905,13 @@
 }
 
 //*****************************************************************************
+// [Dusk]
+const char *NETWORK_GetIWADChecksum( )
+{
+	return g_IWADChecksum.GetChars( );
+}
+
+//*****************************************************************************
 //
 void NETWORK_AddLumpForAuthentication( const LONG LumpNumber )
 {
@@ -1207,17 +1215,22 @@
 	// Collect all the PWADs into a list.
 	for ( ULONG ulIdx = 0; Wads.GetWadName( ulIdx ) != NULL; ulIdx++ )
 	{
-		// Skip the IWAD, zandronum.pk3, files that were automatically loaded from subdirectories (such as skin files), and WADs loaded automatically within pk3 files.
-		if (( ulIdx == ulRealIWADIdx ) ||
-			( stricmp( Wads.GetWadName( ulIdx ), GAMENAMELOWERCASE ".pk3" ) == 0 ) ||
+		// Skip zandronum.pk3, files that were automatically loaded from subdirectories (such as skin files), and WADs loaded automatically within pk3 files.
+		if (( stricmp( Wads.GetWadName( ulIdx ), GAMENAMELOWERCASE ".pk3" ) == 0 ) ||
 			( Wads.GetLoadedAutomatically( ulIdx )) ||
 			( strchr( Wads.GetWadName( ulIdx ), ':' ) != NULL ))
 		{
 			continue;
 		}
+
 		char MD5Sum[33];
 		MD5SumOfFile ( Wads.GetWadFullName( ulIdx ), MD5Sum );
-		g_PWADs.push_back( std::pair<FString, FString> ( Wads.GetWadName( ulIdx ), MD5Sum ) );
+
+		// [Dusk] Store the IWAD checksum elsewhere.
+		if ( ulIdx == ulRealIWADIdx )
+			g_IWADChecksum = MD5Sum;
+		else
+			g_PWADs.push_back( std::pair<FString, FString> ( Wads.GetWadName( ulIdx ), MD5Sum ) );
 	}
 }
 
diff -r 814095fc3091 src/network.h
--- a/src/network.h	Sun Sep 15 23:42:35 2013 +0300
+++ b/src/network.h	Mon Sep 23 22:43:35 2013 +0300
@@ -351,6 +351,7 @@
 
 std::list<std::pair<FString, FString> >	*NETWORK_GetPWADList( void ); // [RC]
 const char		*NETWORK_GetIWAD( void );
+const char      *NETWORK_GetIWADChecksum( ); // [Dusk]
 void			NETWORK_AddLumpForAuthentication( const LONG LumpNumber );
 void			NETWORK_GenerateMapLumpMD5Hash( MapData *Map, const LONG LumpNumber, FString &MD5Hash );
 void			NETWORK_GenerateLumpMD5Hash( const int LumpNum, FString &MD5Hash );
diff -r 814095fc3091 src/sv_main.cpp
--- a/src/sv_main.cpp	Sun Sep 15 23:42:35 2013 +0300
+++ b/src/sv_main.cpp	Mon Sep 23 22:43:35 2013 +0300
@@ -2175,8 +2175,10 @@
 //
 void SERVER_ClientError( ULONG ulClient, ULONG ulErrorCode )
 {
-	NETWORK_WriteByte( &g_aClients[ulClient].PacketBuffer.ByteStream, SVCC_ERROR );
-	NETWORK_WriteByte( &g_aClients[ulClient].PacketBuffer.ByteStream, ulErrorCode );
+	BYTESTREAM_s *pStream = &g_aClients[ulClient].PacketBuffer.ByteStream;
+
+	NETWORK_WriteByte( pStream, SVCC_ERROR );
+	NETWORK_WriteByte( pStream, ulErrorCode );
 
 	// Display error message locally in the console.
 	switch ( ulErrorCode )
@@ -2190,24 +2192,28 @@
 		Printf( "Incorrect version.\n" );
 
 		// Tell the client what version this server using.
-		NETWORK_WriteString( &g_aClients[ulClient].PacketBuffer.ByteStream, DOTVERSIONSTR );
+		NETWORK_WriteString( pStream, DOTVERSIONSTR );
 		break;
 	case NETWORK_ERRORCODE_BANNED:
 
 		Printf( "Client banned.\n" );
 
 		// Tell the client why he was banned, and when his ban expires.
-		NETWORK_WriteString( &g_aClients[ulClient].PacketBuffer.ByteStream, SERVERBAN_GetBanList( )->getEntryComment( g_aClients[ulClient].Address ));
-		NETWORK_WriteLong( &g_aClients[ulClient].PacketBuffer.ByteStream, (LONG) SERVERBAN_GetBanList( )->getEntryExpiration( g_aClients[ulClient].Address ));
+		NETWORK_WriteString( pStream, SERVERBAN_GetBanList( )->getEntryComment( g_aClients[ulClient].Address ));
+		NETWORK_WriteLong( pStream, (LONG) SERVERBAN_GetBanList( )->getEntryExpiration( g_aClients[ulClient].Address ));
 		break;
 	case NETWORK_ERRORCODE_AUTHENTICATIONFAILED:
 	case NETWORK_ERRORCODE_PROTECTED_LUMP_AUTHENTICATIONFAILED:
 
-		NETWORK_WriteByte( &g_aClients[ulClient].PacketBuffer.ByteStream, NETWORK_GetPWADList( )->size( ));
+		// [Dusk] Send the IWAD data as well for the client to compare.
+		NETWORK_WriteString( pStream, NETWORK_GetIWAD( ));
+		NETWORK_WriteString( pStream, NETWORK_GetIWADChecksum( ));
+		NETWORK_WriteByte( pStream, NETWORK_GetPWADList( )->size( ));
+
 		for( std::list<std::pair<FString, FString> >::iterator i = NETWORK_GetPWADList( )->begin( ); i != NETWORK_GetPWADList( )->end(); ++i )
 		{
-			NETWORK_WriteString( &g_aClients[ulClient].PacketBuffer.ByteStream, i->first.GetChars( ));
-			NETWORK_WriteString( &g_aClients[ulClient].PacketBuffer.ByteStream, i->second.GetChars( ));
+			NETWORK_WriteString( pStream, i->first.GetChars( ));
+			NETWORK_WriteString( pStream, i->second.GetChars( ));
 		}
 
 		Printf( "%s authentication failed.\n", ( ulErrorCode == NETWORK_ERRORCODE_PROTECTED_LUMP_AUTHENTICATIONFAILED ) ? "Protected lump" : "Level" );