@rayonfx
I would first do a reset of your Maya Prefs. Reset-Maya-to-Default.html
I would also check to see if any update or virus scanner did not delete any necessary file in the Arnold mtoa install directory C:\solidangle\mtoadeploy\2017
also look into the plugins folder to see if you have the 2 required files there..
Another step would be to un-install just the mtoa plugin in from windows and re-install the Maya 2017 Update 1 and it will re-install the version of mtoa that was shipped with Maya 2017 Update 1.
If you wish to use the latest mtoa plugin from Solid Angle and it still gives you issues, please reach out to their support team, as we don't ship Maya with that version, and we don't know fully if everything works as expected. Since they update and are in the "know" they are the best solution for any "arnold and mtoa" issues on the latest releases.
I look forward to your reply, and best of luck!
Housein Cornell