Creating new wad?????

Trying to install new cars using gpmaster v1.2, when i recomplie wad the new wad is much bigger than the original one and when i run game it crashes back to desktop what am ` doing wrong ????

HELP PLEASE sobpd1

May sound obvious but make sure cars.wad is named cars.wad not car.wad!!:p Otherwise, revert back to backup wad and import new files one by one until you find which one's to blame.