A while ago, ejecting a CompactFlash card on Windows 10 failed with the dreaded message “The action can’t be completed because the file is open in COM Surrogate.”
I was in a hurry, and it was a long time since I bumped into a similar message, so I simply rebooted as I knew that for certainly would fix it.
Next time, these links will help me find which dllhost.exe process to kill:
The Wiert Corner - irregular stream of stuff 