Ran across this nice little gem today. I was trying to copy a file to my personal server that I got from a friend so I could do some work to it. I kept getting the error “unspecified error.”
After a quick Bing search, it turns out this is a known error. In fact, here is the KB article from Microsoft. Short version: copying files across an RDP connection by right-clicking the file on your desktop then choosing copy in the RDP screen (aka clipboard redirection) is not supported. You’ll need to map the drive to the remote computer using the RDP client as the KB article suggests.