Level Editor crashes frequently

[Frontcannon]

The Level Editor has unexpectedly started to crash on a rather frequent basis.

I can start it up just fine, work with it for some minutes, but then it crashes to black, my desktop 'resets' (goes completely black with all the icons popping up again) and Win7 gives me the message that my graphic drivers have stopped working and had to be reset.

I only have this problem with Amnesia's Level Editor, other games like Fallout or Battlefield are running just fine.

Nvidie GeForce 8600GT
Driver v. 258.96 (after updating it through Win7)

Using a Win7 64bit system.