Hello Jerry, I have the same problem (/COMMAND NOT FOUND </gate/digitizer/Singles/insert adder> ) with GATE version 4. Did you find a solution? What was it? Mine is the 32 bit version. CLHEP Version : 2.0.3.2 ROOT Version : 5.20.00 GEANT4 Version: 9.1.p02 GATE Version : 4.0.0 Karthik.