"Err 20: Mechanical malfunction
Within the mirror, shutter or aperture mechanism (most likely), some sort of disturbance, error or lock-up has been detected. This error code doesn’t specify where the exact problem is, but points to the cause being mechanical rather than an electronic gremlin."
W skrócie prawdopodobne uszkodzenie mechaniczne: lustra, migawki lub mechanizmu przysłony.