Mountain Lion and Mission Control

This happens to me too - I think the problem is somehow related to the screen saver and system sleep. There's an easy remedy:

Go to your System Preferences --> Desktop and Screen Saver. Click on the "Screen Saver" section, and click "Hot Corners". Set one of your hot corners to "Start Screen Saver".

Next time Mission Control fails, just point your mouse to the "Start Screen Saver" hot corner, and wait for the screen saver to start up. When you start working again, Mission Control will be back to normal.

It doesn't fix the problem, but it's whole lot faster than restarting or logging out each time it happens.

Although now I've reread your question, and I'm not 100% certain we have the same problem. When you say "Mission Control freezes" do you mean that you successfully activate mission control, but then can't get out of it? Or do you mean that you can't get into mission control at all (I can't get into mission control at all - nothing happens).

It's the same problem then. The screen saver trick should help you.

I have this problem with mission control. It simply goes away without notice. It also rerurns without notice! The problem is so flaky that almost anything will apparently cure it. Essentially, do anything and mission control will return to service. I know this is an entirely illogical and irrational post - but so is the problem.

This is a bug. I am not sure why it happens but restarting the dock (the name of the process that includes lots of user interface things like Mission Control, the Dock and Expose) is the easiest workaround.

You can restart the dock by going to screensaver, logging out or some other similar things. If you'd rather not have the hot corner trick (I think they get in the way) just open the application called "Terminal" (in the Applications>Utilities folder) and type:

killall "Dock"

then hit the enter key. The dock restarts, and mission control works again.

Thanks but this bug is so flaky that almost anything may - or may not - restart Mission Control. Sometimes, I just wait for it to come back without doing anything at all. Best way to live with this is to leave a particular app in each window then select the app from the dock. That will take you to the desired window even while Mission Contro is still sleeping.

This solved my problem too. Hopefully there will be a upadate soon to fix this issue!

Thanks for the help!

I waited for 10.8.1, which solved the Exchange problem, to update my IMac. Now I have the same problem as described. Mission Cotnrol randomly stops working. I will try your workaround. Wonder if it is related to my usage of a second monitor. The old issue with the background picture of the second monitor randomly not showing when waking up, persists as well.

No, it has nothing to do with having a second monitor. My guess is that it depends on which graphics card you have. I never experience this problem on my iMac at work (2011 model), which has a second monitor. I only see it at home, which is an older iMac (mid 2007) with only the internal monitor. And yes I do still see this with 10.8.1 - I think the 10.8.1 update is only for high-priority, major issues. Since this is a small problem (still annoying, but it won't cause data loss or impair your ability to use your mac, and the workaround is easy) it won't be fixed until a later update.

Have the issue on a 2012 IMac but not on 2012 MacBook Pro 17".

i have the same issue on an iMac summer 2011. 3.1 GHZ Intel core i5

AMD Radeon HD 6970M 1024 MB.....

hope that this screensaver active corner trick does work:-) its really annoying otherwise...

Thanks. It works.