1. Get all the GSC's you modified from your patch, and put them in their proper folders (create a maps folder, inside that a mp folder, inside that a gametypes folder, then your GSC's)
2. Go to C:/Program Files (x86)/Activision/Call of Duty 4 Modern Warfare/Mods. Create a new folder there called "TestPatch". Put your "maps" folder from step one in there. Then, start cod4 MP. Go to Mods, and select TestPatch, and load it. Once it loads open your console and type:
/developer 2
Hit enter.
3. Start a game and with the dev mode it should tell you your errors.