>Just out of interest, which framework is it?

It's VMP. The developers there think the problem is due to me having an older version as they initially were able to duplicate the problem, but made a data change (suggesting an aberrant record in the semaphore locking file was causing the problem) and now they no longer have the same problem.

I am awaiting feedback from other users to see if they have the same problem. If not I will upgrade to the latest version and hopefully that will solve the problem.