Profibus Trouble - Output turns off when I change the program

Dear Sirs, on the AC900 with S800 in profibus I have an engine that is activated via profibus, when I make any changes in the program like changing a constant, the folder remains green but when I give the command change obejects the engine stops. How to increase the time on the master or on the profibus slave so that the engine does not stop when any changes are made? Can you help me?