Error 20 on 5D Mark II

Two days ago I got the dreaded Error 20 on 5Dmark II while using 100-400mm lens. I have never seen it before and I have this camera for 2+ years. I tried turning off the camera, taking the battery out waiting few minutes and shooting again. I continue getting the Error 20.

Then I switched the lens to 24-105mm, took out the battery and was able to take one shot but error came back again. Turned it off, switched back to 100-400mm and was able to shoot a few shots without getting error20.

I have not used it since. What to expect here? Do I need to send it in and get it repaired or wait till error 20 comes back again. Not sure what to expect and/or what to do.

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2ShootDigital