I think I may have found the solution. I'm not entirely sure, but, it seems to be working so far and it's survived a couple of reboots. The intermittent nature of the issue makes it tough to be certain until after I've lived with it for a while.

Code:
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Terminal Server Client]
"DisableClipboardRedirection"=dword:00000000
"DisableDriveRedirection"=dword:00000000


If this really is my solution, it's odd to me though, for these reasons:

- Those registry entries didn't exist at all on the computer to begin with. I had to add them.

- The setting is called "Terminal Server Client". Also all the web sites which talk about those settings also say that it must be on the client PC. In this case, client means the local PC on which you're running MSTSC. But in my case, I added those settings to the SERVER computer, i.e., the one running remote desktop services, i.e., the remote work PC.

Only time will tell if this truly solves the problem in the long term.
_________________________
Tony Fabris