When right clicking more than one item off of a tool rack, receive the following crash report.

http://pastebin.com/wsF6MTXh

May very well be InvTweaks fault, but you're alive whereas InvTweaks is...not so much.

EDIT: Narrowed this down to an interaction with Dual Hotbar mod. Specifically with a CFB tool rack, if I'm on the second row of my hot bar and right-click an item back onto the tool rack, I'll get this error. If I'm on the first row (vanilla) of the hot bar, it works fine. I'm removing Dual Hotbar from my pack, as it hasn't been updated in ages.