My 5DII has been perfect with the 24-105/4 and the sigma 100-300/4, and the sigma 70-200/2.8 OS, and it worked fine with the 50/1.8 I bought here. However, I have not used the 50/1.8 for about two months. Today, when I put it on, it did not AF. Am I doing something wrong? Have I turned anything wrong? I tried with the other lenses and it is perfect. Any advise before I go crazy.