Welcome to the Forum, Mohammed. I hope that you can find some help here.
It would be useful if you would post more information about your specific PLC.
My guess is that it's a Siemens device, because the German word "Fehler" means "Error" in English, and the specific error code you mentioned "UAFEHL" appears in a user manual for a Sinumerik 840 machine controller.
Please post as much useful information as you can gather about the controller, the system it is controlling, and how the error code appears to you.