We are running Windows Server 2008 R2, Remote Desktop Services.
The server is a Dell R410, Intel Zeon E5520, 2.26GHz 8M cache, 8GB 1066MHz Dual Ranked RDIMMs, Advanced ECC mirror.
Out of the factory the memory was set to Mirror, so only 4GB was available. I thought, that's what was crashing the system. So I changed it to Optimized mode, and now all 8GB are available, but it still got stuck this morning.
All remote users froze, and could not reconnect. Luckily I was logged in via the console at the time. It showed that 4GB of memory was still available, and the CPU was not too heavily utilized.