Hi Henry
Funny enough, I had a client call me today with the exact same error message, when trying to purge a Shipment Audit List (using a really old version of Inventory).
When I went to make a backup prior to running DIC, it found 14 files in use and there was no other Adagio user on the Terminal Server. This indicates to me that the problem is that the system thinks a file is in use when it really isn't.
If this is the case for you, try rebooting your computer and if that doesn't work, reboot the server. I'll bet that will fix the problem. My client reported a power outage yesterday, and that might have been the culprit; I'd be curious to know if something similar happened there.
I would still run DIC just to be safe and Rebuild if necessary.
Steve