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It sounds like the link to your Logic app in the Dock is broken - hopefully not the application itself.
Navigate to the Applications folder and look for Logic. Is it called Logic.app or Logic 9.1.app... or something else?
Is Logic in the Applications folder or a sub-folder within that folder?
If you find it there then drag it back in to your dock. (You can remove an icon from the dock by dragging it from the dock and releasing the mouse button...
I'd also recommend running software Update to make sure you have the latest versions of OSX and Logic.
Hope that helps