my 80-200/2.8L tends to invite error 01. It was very apparent when i was in japan, where error 01 showed up almost everytime i tried, and another thing was that looking through the viewfinder, it was very dark.
there was a thread on error 01 and a fellow CSer mentioned about going into liveview for the aperture blades to realign or something like that. It worked initially but thereafter it got darker and darker then error 01.
coming back to singapore, i wanted to send for servicing but after mounting, everything was back to normal. So i might just send it in for servicing rather guess when it's going to error 01 again.
i think sending yours in would be the better option, rather than guess-working. it can get very irritating. :sweat: