The main problem with that foot is what you've already discovered. It interferes with the automatic presser foot height adjustment. That's why you get the error message when you turn the machine on with it installed. If you really are dead set on using it, try turning the adjusting screw to make the foot higher. If you get it high enough to stop getting the error message when you turn it on, then it should work correctly.

Note, however, that the QV foot included with the 12000 is identical to the large "toe" on the 11000 free motion set. The QC and QO feet perform the same function as the small metal toes, and they are all made for the 12000 - a much better option! You really need to be careful that the foot does not bottom out, because if it hits the plate repeatedly it could do some damage to the automatic presser foot lifter/adjuster.