Microeditor 5.5 / error 161

[rntech]

The file ****.sf has changed , if changed only by writing file flags project is unaffected.
Do you wish to delete all the segments in the project file that refer to this file.

options yes ,no or cancel.

Does anyone have any suggestions to eliminate this error.
The user is on a network and was all ok last week.
the Drive that Microstudio refers to is valid and is established via a login script.

I have even restored the files from backup from the last time it was ok.

Any Clues?