That would have been my next place to look. If you use QIT as the mass analyzer and an explicit resolution, even if that resolution value is quite narrow (though constant over the entire m/z range), we don't show mass error. You need to use one of Centroided, TOF, Orbitrap or FT-ICR to even have the option to show mass error.
Thanks for posting your solution to the support board.
--Brendan