Alarm 25201 is secondary alarm caused by 300504 and 300508, which 2 alarms showing your spindle motor measuring system problem. You can check the spindle encoder cable, and check encoder problem. I attached Siemens Diagnostic Manual, check alarm # and following the steps  

I suppose your machine using OEM spindle motor also possible all-in-one or call motor spindle , external encoder . If you want to compare, you can think if it possible to exchange encoder and encoder cable between 2 machines (exchange one at the time) 

PS: You may make a mistake---the CNC brand Fanuc (Japanese Company)  instead of Fanuk     

rezamohebbi

I need help. I have two horizontal milling machines, the first machine with Fanuk 18 control system and the second machine with sinumerik 810d control system.  Both machines do the same machining process, but the Siemens machine regularly gives spindle alarms, 300504, 300508, 25201, etc., while working in the same condition as the Fanuk machine without alarm, please help.