We fixed it by starting a session of Revit double clicking the file in it's folder vs. opening the file from within Revit.
We do a bit of programming here with Addins and we think the addin has caused the issue. The addin won't load if you start Revit by doublle clicking the filename.
Opening the Revit file with a dobbleclick does the trick for me... Strange! Maybe someone from Autodesk would like to comment the subject?
I came through the same problem after installing the Microsoft .NET Framework 4.5 with Visual Studio 2012. After removing it and reinstaling the previous version of the .NET framework (Version 4), everything went fine.
There is finally a fix for the issue.
We seemed to have solved it in Revit Structure 2013 by installing Update Release 3 found here:
Not sure if there is a similar update for Architecture
I had one issue on one of our computers that we had the Arch Revit loaded. Had to go get a different SP for the Arch Revit Only.
Once I got the Service Packs ran, all three were working correctly.
Thanks for the fix !
I still have got the problem While I'm working on Revit 2014 SP1.... Rolling between Ribbon sizes doesn't recover the buttons (tough I remember it worked on previous releases)
neither " press ALT + M + FM this will essentially press the green check to finish your command. Or use ALT + M + XM to Cancel."
nor setting new shortcuts nor refreshing all UI panels recover the buttons....
I don't know what else I can do to finish/cancel my floor !?!
 Freeeeedoooom !
Clicking the little save file button and then cancel has finally cancel the whole editing mode without having saved the file locally....
So it's the only working solution left with 2014 sp1 !