I reckon the last mod you used has a problem, and seeing as the PLR stores info about which mod was run last, it may be crashing rF.
Open your PLR file and edit the following lines;
Scene File="GAMEDATA\LOCATIONS\CroftCircuit\CroftBTCC\CroftBTC C.SCN"
AI Database File="GAMEDATA\LOCATIONS\CroftCircuit\CroftBTCC\CroftBTC C.AIW"
[ DRIVER ]
RaceCast Email="" // The email you are registered with on racecast.rfactor.net
RaceCast Password="" // Your password on racecast.rfactor.net
Team="ZR Racing Team Green"
Original Driver="Buster Timms"
Birth Date="22 April 1981"
Delete the bits in red that would be in your PLR file. I dont know if its important or not, but keep the quotations in. I know the top few lines relate to the last track used, but it doesn`t hurt to be thurough.
Example being the top line. It would read;
EDIT: Doh! I just read your post properly and it seems this may not help you.
Your best bet might be to make a new user, and copy the new PLR file over to your name. If the game then works, you know your old PLR file is corrupt.
You`ll lose all your settings, so keep your old one as a back-up. Then start re-entering your game, FFB, graphics settings etc bit by bit. Keep checking the game now and then incase something you copy over has fluffed the new PLR file up. At least then you`ll know what has done it.