[Steve Kuffrey]

Files becoming corrupted or unable to be used can be caused by any number of issues, here is a short list:

-adding or removing other software on your PC.
-power surges.
-turning the PC off improperly.
-adding or removing hardware.
-a virus.
-a fragmented hard drive.
-having your PC lockup or freeze.
-improperly closing a program.
-hardware failure(that has either shown itself or maybe not yet).

Just to name a few. What caused your problem? I have no idea, it may have been OOTP or it may have been some other issue. One thing is for sure is that it is always a good idea to make regular backups of your league folder(s).