I have found this issue may not be due to a problem with the Remote Desktop tool but an issue with windows 8.1.
This is with the Windows 8.1 release from MSDN/Technet
• Configure Network Level Authentication
1. Open Regedit.
2. In the navigation pane, locate and then click the following registry
subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
3. In the details pane, right-click Security Packages, and then click Modify.
4. In the Value data box, type tspkg. Leave any data that is specific to other SSPs, and then click OK.
I was left with “” and tspkg
5. In the navigation pane, locate and then click the following registry subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders
6. In the details pane, right-click SecurityProviders, and then click Modify.
7. In the Value data box, type credssp.dll. Leave any data that is specific to other SSPs, and then click OK. (This was already in my config so I didn’t change it)
8. Exit Registry Editor.
9. Restart the computer.
Once done, ASG RD worked fine for all my connections again.