RDP problems in Vista

We regularly use RDP to connect to various servers and workstations for support purposes, all routers and firewalls are setup for this and in XP everything if fine. When using Vista, however, the connection is made, passwords accepted and the desktop appears. But you cannot interact with it, no clicking on icons, nothing. After a few seconds the connection fails. Imedietly moving to an XP machine and retrying the connection works, everytime. Has anyone else experienced this, or found a fix?