Hi Zyrus -
Currently The Animation and Rigging Toolkit has not been officially tested with Maya 2015 when it is we will update teh official ART forum thread, here, this is also a great place to check to see if anyone has had similar issues and whether you have the most up to date version of the Toolkit.
All that being said, my first question is have you gotten the newest version of the toolkit from that forum thread, also available, here.
Let me know if you have tried this newest version and we can continue to work on this issue with you,
Eric Ketchum