Mission Control no longer runs

Back up all data.

Hold down the option key and select

Go ▹ Library

from the Finder menu bar. From the Library folder, move the entire contents of the subfolder "Caches" (not the folder itself) to the Trash, then log out and log back in. Empty the Trash. Test.

If the problem is not solved, open the Library folder again in the same way and move the entire contents of the subfolder "Preferences" (not the folder itself) to a new folder on the Desktop (not to the Trash.) Log out and log back in. The account will then be pretty much in a clean state. Test. If you can still reproduce the problem, then put the Preferences folder contents back, replacing any that were created in their place, log out, and log in again.

If you can't reproduce the problem in the clean state, then start putting things back in the Preferences folder piecemeal, starting with items that seem unrelated to the issue. I can’t be more specific. After each group of items, repeat the log out/log in cycle and test. At some point, the problem may reappear, in which case you know that something in the last batch of files you restored is at fault. If it never reappears, the problem is solved.

After moving the files above to the Trash should I reboot instead of logging off to free up the file?

Yes.

It's not clear to me what you've done or what exactly the problem is. I suggest a fresh start.

Back up all data to at least two different storage devices, if you haven't already done so. One backup is not enough to be safe. The backups can be made with Time Machine or with a mirroring tool such as "Carbon Copy Cloner." Preferably both.

Boot into Recovery mode, launch Disk Utility, and erase the startup volume with the default options. This operation will destroy all data on the volume, so you had be better be sure of your backups. Quit Disk Utility and install OS X. When you reboot, you'll be prompted to go through the initial setup process. Don't transfer any data from your backups at this stage. Create a new account.

After logging in to the new account, restore your documents and media libraries. Reinstall your third-party software cautiously. Self-contained applications that install into the Applications folder by drag-and-drop or download from the App Store are safe. Anything that comes packaged as an installer or that prompts for an administrator password is suspect, and you must test thoroughly after reinstalling each such item to make sure you haven't restored the problem.

I was having the same problem: Mission control wouldn't launch for my account but would for other accts on the same computer... nothing interesting in the logs.

After reading through this thread the following simplified steps fixed it for me:

1. Move both com.apple.dock.plist and com.apple.spaces from ~/Library/Preferences to a safe backup location (e.g.: the Desktop)
2. reboot

Problem solved! Thanks for the final update, DDTriGuy!! com.apple.doc.plist was the key. Removing the entire ~/Preferences directory was not required (for me, at least).

Thank you so much TikultiNinurta and also DDTriGuy for the fixes.

I've had this broken Mission Control thing for over a year! (On Mountain Lion, Mavericks, and now on El Capitan. None of the updates fixed it.) I had also upgraded to a new Mac and migrated to it with migration assistant, but this issue still persisted after the move. I guess my preferences were migrated during the move, bringing with it the corrupted files that were stoping mission control running.

My issues:

• Mission control wasn't opening/working at all for me.. I could find the app in my applications folder, but could not run it via clicking or with any of the other shortcuts wouldn't bring it up. It also didn't appear in my running processes in activity monitor when i tried to open the application. It would work in other user accounts though.
• Also, the "show desktop" 4 finger gesture wasn't working for me (all other gestures worked fine).

Fix for me:

• Removing com.apple.dock.plist and com.apple.spaces from YourUsername/Library/Preferences/ then promptly restarting.
• In addition to com.apple.spaces.plist, i found 3 'empty' plist files with some numbers and letters at the end of the file names (com.apple.spaces.plist.hP9fFgH, com.apple.spaces.plist.BkuoARm, etc). These were all zero bytes with various dates from the last 18 months. I suspect these have something to do with the corruption issue. I also deleted these before restarting.

*** Note I initially tried to fix it by removing com.apple.dock.plist from MacHD/Library/Preferences/. This didn't work because that isn't my USER preferences folder. I had to come re-read this forum again and search for the plists in terminal before i realised what I was doing wrong. The full path for these preference files is MacHD/Users/YourUsername/Library/Preferences/. You may need to enable show hidden files to see this in your User folder because for me User/Library was a hidden folder (i.e. its grey font but you can open it once you enable hidden files).