VPF 9.0 with all tables in DBC's

This last week we have had numerous error messages in our applications where a
"FPT File is Missing or Invalid" error is reported.

Nothing has changed in the application and have not had these errrors before. Now all of a sudden it is happening quite frequent. At first was speculating that an issue was with some interuption in the network since we experienced some severe storms ect. Server is protected quite well and I am having a problem trying to figure out what is causing these errors. It is not consistent with a particular table, just that it always is a Memo field problem.

Can anyone share with me suggestions as to what to look for in trying to find a solution. We did recently switch over to "Sophos" virus protection and the beginning of this week sat down with network administrator and made sure that our tables were being excluded from scanning, thinking that there might be some kind of issue there. I was assured that they all are now (originally were not all, but some of them). I am not able to determine any user who can be linked to the problem.

Any suggestions would be greatly appreciated.

Thanks in advance