Kenko extension tubes

I`ve used EOS Utility before with my 100mm L macro lens and I was able to control the focussing with the computer. I have just purchased a set of Kenko automatic extension tubes and I`ve found that with them attached I can move the focus point in one direction only! Taking the tubes off and just using the lens was fine. Has anybody else found this? Any ideas what might be happening? (I`m using a 5D4.)