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Every so often (usually when I have a ton of windows open) I trigger mission control and I get this:

enter image description here

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.

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You can do a couple resets to the computer to see if it resolves the issue.

  1. Disk utility (application) > select 'Macintosh HD' on the left-hand column > and click VERIFY disk under FIRST AID.

This takes about 2 - 3 minutes and will let you know if you have a corrupt hard drive which might be causing that issue

  1. Reset PRAM -- Shut computer down > hold down: p + r + Command + Option > with these four keys held down, proceed to hold down the 'POWER' key as well in the top-right hand corner of the keyboard. > hold down all 5 keys until you hear TWO sounds come out of the computer.

It'll be that familiar chime sound that it makes upon starting up normally

These steps work for all Mac computers -- let me know if this works

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The issue hasn't happened in a long time. If it happens again I will let you know if it works. – Chris Apr 29 '13 at 20:17

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