I had the same problem after installing Bugfixer in the same R:TW copy where I had the Community Mod. It seems that some of the files Bugfixer installs are the mount database. Fortunatly, Bugfixer comes with backups (the "original data" folder). If BI and R:TW data folders are seperate, replacing the bugfixer files with those in the "original data" map will resolve your problem. If BI and R:TW data files are shared, I am afraid you will have to reinstall the entire game.