I have the exactly the same problem.
My configuration is:
Pentium D; CPU 3.60GHz; RAM 2.00GB; Two LCD monitors (1 running FSX, 1 running Plan-G); Windows XP Professional w/SP2; FSX w/SP2; FSUIPC dll.
When occurs, and it occurs everytimes I use Plan-G, it is complete, let me say, I need to restart the computer at all.