After opening the back of the MicroTech case (possibly to replace the XLR panel or to make repairs, etc.), make sure that the two screws that hold the plastic case together have not been overtightened.
Overtightening these screws tends to bow the face of the MicroTech inward, causing the buttons to stop working (typically, they get stuck down).
Release the extra pressure on the face of the MicroTech by slightly unscrewing the rear-panel screws. This should fix the problem.