I went to the Galápagos Islands last month using the above combo with no problem for 4 days and on the last day I let my wife use it while I used my Sony FS700 to do super slo mo videos. It was a cloudy day with light rain, the Sony got a bit wet but functioned with no problem and so did the 5D Mk III. I dried them both off afterwards and they were both working fine too the day after that. Then 2 days later when I got to Cuzco, Peru (it was cold but sunny), I started getting the Err 01 messages occasionally, then a few days later, I just got the Err 01 message constantly and the lens stopped functioning. Luckily I have a Zeiss APO Sonnar and Planar which were working totally fine, so I thought the problem was with the lens. But now that I'm home, I tried out the 24-105mm with my 5D Mk II and to my surprise, it's working totally fine, while I still got the Err 01 with the Mk III. Has anyone here had a similar problem with the 5D Mk III and 24-105mm? Not sure if I should get a new one or try to get it repaired. Any suggestions? Many thanks in advance.