We are experiencing a really weird VPN problem! We are having a RDP issue though VPN client and L2L VPNs connected to one particular VPN concentrator. The VPN's are working fine, other than RDP. When using the VPN client or the L2L VPN, we are able to RDP to a particular server. We get the login screen and can enter the crediantials, but the screen then freezes. As soon as you move the mouse on the client machine the windows screens then continue to load. When you stop moving th mouse, the screens freeze again. Move the mouse again, and everything works again. So, basically, as long as you keep moving the mouse the RDP session will work.
We have tried another server, which works fine. So that points the guilt finger at the server. But when we try a different VPN concentrator, configured exactly the same as the first one that RDP doesn't work through, it works fine! So that seems to remove the server from the equation and point blame at the VPN concentrator. Now we have a stale-mate situation, where the problem points at both the server and the VPN concentrator.
I have read many of the other threads and checked the MTU sizes, which seem to be. We have set the client and server MTU's lower (1300) than the VPN conc outside interface MTU (1500), but that had no effect.