OK - it has been crazy busy for a while, so re-indexing hasn't happened for a couple of months.
Just tried doing the 10 primary files we always do and received the following errors:
 
You have tried to access a file that has not previously been opened or the FNUM passed was 0.
 
An error has occured trying to open BKICMSTR.B -12  
  (the file of course exists and as admin, I have full rights)
 
An error occured while attempting to open the new file.  The current file has been restored.
 
Got a clue?

UT-C