Why did my Command + V (to paste) suddenly stop working?
I had the same issue in Mac Excel 2011 I am still using. 

-Right click on the Paste icon in toolbar, choose Properties...
-Next screen, click Keyboard... on right hand side
-In "Press new shortcut key", add command+v.

That worked, even though command+v was already in list of current keyboard keys for Paste function. Hope this helps