Can't cancel rendering

[vermu]

I have had this annoying problem with 3dsmax 2012 and vray2. When render starts the render progress window pops up. If I have material editor window or render setup windows on the location where render progress window pops up my material editor and render setup window
freezes. I can't close material editor window or render setup window because they don't respond at all. render progress window happens to be under these frozen windows and that's why I can't cancel my render. It there any work around for this? I usually avoid moving those two windows where render progress window pops up but you can't remember it all the time.

[Svetlozar Draganov]

This is how Max behaves, once rendering is being started all windows except Frame Buffer and Render Progress are not accessible.
However they(FB and progress windows) should pops up at the top leaving all existing ones at the back but it seems that this is not the case in your environment.
Have you tried to cancel the render with ESC-key from the keyboard?