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Over the course of my ownership of a MacBook Pro running Lion, I've had an extremely odd bug occur somewhat sporadically. It rarely occurs, but when it does, the following effects become apparent:

  • I can no longer switch spaces using trackpad gestures, but I can using keyboard shortcuts.
  • Dashboard becomes inaccessible without using Mission Control; only the main spaces can be moved through with the shortcut keys.
  • When moving between spaces, all easing is gone from the transition animations. The animation seems more like it was in Snow Leopard and prior.

I really have no idea what could possibly cause this, and even though it's only happened to me four or five times, it's quite annoying since I use Spaces a lot. The only way I've found to resolve the problem was restarting the entire OS. Has anyone else had this happen to them? If so, do you know of a fix?

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I eventually managed to find the issue by poking around in console. I got the following error messages:

Dock: kCGErrorIllegalArgument: _CGSFindSharedWindow: WID 6963
Dock: kCGErrorIllegalArgument: CGSGetWindowTags: Invalid window 0x1b33
Dock: kCGErrorIllegalArgument: CGSGetWorkspaceWindowGroup
Dock: kCGErrorIllegalArgument: CGSGetWindowOwner
Dock: kCGErrorIllegalArgument: CGSGetWindowBounds
Dock: kCGErrorIllegalArgument: CGSSetWindowListSystemLevel: Failed
Dock: kCGErrorIllegalArgument: _CGSFindSharedWindow: WID 6963
Dock: kCGErrorIllegalArgument: CGSGetWindowTags: Invalid window 0x1b33
Dock: kCGErrorIllegalArgument: CGSGetWorkspaceWindowGroup
Dock: kCGErrorIllegalArgument: CGSGetWindowOwner
Dock: kCGErrorIllegalArgument: CGSGetWindowBounds

While I'm not positive what causes these, sure enough, restarting the Dock using killall Dock did the trick. Though I still have no idea what causes this in the first place, this is at least a fix for the rare problem.

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