Eudora Mail Problem!!!!!!

I have been having this program with Eudora Mail clients. It seems that certain inbox's are being deleted or become corrupt when users start up there Eudora. Also certain mail messages become unreadable, also the subject of the messages are different than what the content of the message is.
I have scanned all pc's for viruses and nothing is found. I have also tried deleting the .TOC file and let Eudora recreate it on opening of the application. Still nothing.

Any help would be great!! Thanks!!

We are using Eudora 5.1

 

Help?????????