RDS 2008 - random disconnect and prompt for credentials

Hi guys

I have this issue in RDS 2008 where users keep getting disconnected and prompted for credentials.

I have checked:

• Configuration Properties > Sessions "Active session limit" to Never (force it by overriding user settings).
  This has been set through group Policy
• The licensing appears to be correct with no errors
• HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server
  fDenyTSConnections and all RDSH servers have set to 0.
• No HTTP redirection on default web site.

I checked a few other things, but nothing has prevailed.

I found the Event 4634 where accounts were being logged off on the AD server.

Im not too sure what the cause is, anything to look for?

Thanks
NN