Hello Dears ! From a couple of days I recently observe the problem with my mamiya

at the beggining it was problem with shutter - sometimes firing , sumetimes not. I am using it with the film back and 120 films. From a few days the camera do not answear

the only communicate as the response for pressing the shutter is err-02 I would like to know what is it ? It did not fall down and I think technicaly is ok. What is interesting when I detached the lens it and press the shutter , the film is transporting in the back , shutter is firing and everything seems to be good, when i connect the lens the lens works ok - perfect AF as in the mamiya and after when I press the shutter err-02

Do somebody have any idea what can cause this problem ?
Thank you in advance for your repplies
Oskar