Every so often (usually when I have a ton of windows open) I trigger mission control and I get this:
I have to do a complete restart of the computer in order to resume. This happened to me on both OS X Lion and now OS X Mountain Lion.
I'm running a Mac Book Pro 2.53 Intel Core i5 (with 8 GB of memory). It's plugged into a 27" Cinema display via the display port. To my memory this has only happened when plugged into the Cinema display.
I'd really like this to stop happening, so I'd love to know if there is a fix for this.