W7 unresponsive when loading something in vvvv

i experiencing some problems on a windows 7 64 bit machine.
windows gets totaly unresponsive when a frame takes a while to compute (eg when reading big files / creating meshes). cursor still can be moved.
the problem does not occur on my 32 bit system.

i allready tried to change priority or isolate vvvv on a specific core via task manager but also via SetProcessAffinityMask.

what do you think?

please see if this also happens if you have no Mouse (System Global) in use. note that there is one inside of Camera (Softimage Transformation)

thanks joreg i will test this on monday, dont have the pc here.