How to run the Geant4PEPI in the multithreading mode

Geant4PEPI is a geant4 simulation of an Edge illumination. The authors are L. Brombal and N. Poles. I run the program in a single thread and it can work. But It cannot work in a multithread mode. The code about GPS cannot run properly in the multithread mode. And My other programs can work in multithread mode. I have no idea about this issue and I hope you can help me. Thank you.