"Hung" files

Occasionaly a drawing file will get "hung" - meaning that when you try to save it you get an error message that it is open in another application and to close it and so on.  We usually save it with an "a" appended to the file name.  Sometimes you can come back to the offending file; most often we have to reboot the server to clear the problem.

Of course, the file is NOT open anywhere else, the preview pane is turned off in Explorer, there are no DWL files associated with it - have even tried closing AutoCAD (ACAD 2011) and deleting/renaming to no avail.

ACAD 2011, Windows 7 SP1 - the server is Windows Small Buisness Server 2011 Standard, SP1

Any suggestions would be welcome

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