I've had the above problem on my windows 2008 64-bit machine recently and the suggested fix http://support.microsoft.com/kb/911720 didn't work.
Basically, the problem is that the registry is wrong. So, the solution was to edit the registry...
- Go to command prompt and type regedit
- When regedit opens, locate HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\aspnet_state
- ImagePath Data was %SystemRoot%\Microsoft.NET\Framework\v2.0.50727\aspnet_state.exe so altered to %SystemRoot%\Microsoft.NET\Framework64\v2.0.50727\aspnet_state.exe
- Go to Services and start ASP.NET State Service
Ta da!!!!