problem with RDP to win7 client

[exmos]

we have an LX1000, connecting via rdp to other OS's running on a VMWare ESX4 server. Connects to any OS trouble free apart from a Win7 virtual PC - when trying to access the 'start' menu, the menu appears but flashes rapidly as if being clicked 100 times per second. This has been tried on 2 Win7 virtual PC's and same problem; are there any known issues with RDP to Win7? Any suggestions