If you are using VFP tables directly instead of views and rollback of transaction is often the index file corrupts. (I have started using views for each such file)
If you are using Novell netware with trasaction tracking on, using novell TTS in Foxpro does corrupt the file often ( I have this expirence with Novell 4.11 and foxpro dos 2.6 which was solved by keeping daily transaction files seperate and creation of new index file at end of day for daily files when tey were transferred to main files)

HTH
Rajesh