With the new Microsoft patches for Spectre and Meltdown, many will see that they can no longer shadown their users with Terminal Server / Remote Desktop Services, all they will get is this:
“Shadow error: Unspecified error”
Only solution, as of the time of writing is to install theese KB’s on their respective system:
Windows Server 2012 R2 (KB4057401):
https://www.catalog.update.microsoft.com/Search.aspx?q=KB4057401
Windows Server 2016 (KB4057142):
https://www.catalog.update.microsoft.com/Search.aspx?q=KB4057142