Recently, I ran into a scenario in GP 2013 where the depreciation button was grayed out and the user couldn’t select or change the books available for depreciation. GP had hung in the middle of running depreciation.
The fix was pretty easy and is detailed in https://support.microsoft.com/kb/852399
In a nutshell it boils down to clearing the FA40203 temp table with the SQL command:
DELETE FA40203