Canon 40mm pancake lens issue

Yesterday I went hiking with my wife. I decided to put the new Canon 40mm lens on a T2i for her. That would be light and a good test for travel. I took my Mark 5D iii with a macro lens.

At the top of the trail, I asked my wife for her camera to take a picture of the lake. The lens would not focus. I checked and the lens was set to auto focus. I turned the camera on and off. The red light lit up in the view finder, but the camera would not focus. Then I tried putting the lens on manual focus and that did not work either.

This morning I put the lends on my Mark 5d iii and it worked fine. I then put it back on the T2i and it works as well.

As I recall, the new firmware for the Mark 5D iii had a fix for this new lens. Are there compatibility issues with older cameras?