Assuming you’re still getting the error and not just looking at historical errors in BugSack/BugGrabber (alt-click on the minimap/broker icon to clear them).
If you’re on Windows, grab Notepad++ (TextMate if you’re on Mac)
Do a Find in Files search (CTRL-SHIFT-F) for UPGRADE_BONUSES
On your WoW directory [make sure it’s the one referenced from wherever you launch the game].
Filter it against *.lua files and make sure In all sub-folders is enabled (might want to enable hidden folders in this instance too).
