Dropping Data???

I'm completely confused over this one.

I've been using web assist data assist for many years on many, many projects and I've NEVER run into anything like this.

Developed a product database for a client. Fully tested the online data assist forms and everything worked fine. Had the client upload their data. After many hours of uploading, the client discovered much of the data they input was not retained. The individual records were there, but the information within was not.

I have fully tested and retested on my system (Mac using FireFox 5 browser) and cannot duplicate their issue. Everything seems to work perfectly fine for me. They are on an older PC using IE (can't seem to tell me the version). Could that be an issue? I know there are display issues with older browsers but I've never run into form issues in which everything appears to function properly but data is just lost.

Suggestions for troubleshooting??? Please Help!