"Arm Must Be Left" Error

Well, after finally getting the machine set back up after clearing all the memory (by accident, thought I was clearing the tool and fixture offsets - but that's a whole other story). Now I'm getting an "arm must be left" error when I try to enter the MDI. I can do TC,1 and everything works. At a loss.

1996 Fadal VMC15 with 16 ATC

Please help!

Thanks,
Andrew