Rudy, run CUILOAD and see if EXPRESS is listed. If not, then browse to and load 'acetmain.cuix' in the Support folder where acad.cuix is located. If that still doesn't work, then run 'Add or Remove Features' for your AutoCAD MEP from the control panel and reload Express Tools. If it's already checked, then uncheck to unload, then recheck to reload.
Bob Felton Autodesk Product Support Autodesk, Inc.