User Portal RDP Connection: Protocol Security Negotiation Failure

Question

When trying to initial an RDP session from the user portal, to a 2012R2 server or a 2016 RDS server, whether configured for RDP or TLS,I receive the following error: 
 
 Error: Protocol Security Negotiation Failure. 
 
 I can't find anything in the logs to lead me anywhere, and would like to get this resolved. Any suggestions? 
 Here is the Bookmark config: 
 
 Here is the user portal:

And the error:

lferrara · Accepted Answer

Scott, 
 how is the RDP configured on your Windows Server? I mean is the Network Layer Authentication Enabled? 
 Thanks

lferrara · Answer

Try to remove the "Allow Connecitons only from ..........." and see if it works.