When trying to connect in HTML5, you get this error:

Network Level Authentication


RDP: recv failed 127.0.0.1:XXXX

CredSSP required by server!


Credssp is not a TSplus component but a Microsoft component.

This component needs to be activated in the majority of connection cases on recent systems.  
This is not the case with Novell.
To disable Credssp, proceed on both server and client side:

1. Run gpedit.msc
2. Go to Computer Configuration> Administrative Templates> System> Credentials Delegation.
3. Double click on 'Encryption Oracle Remediation'.
4. Click on "Disable" before confirming with OK.
Then open a DOS command prompt and enter the command: gpupdate / force