Is it my lens or the teleconverter?....very odd

I have a 7D with the 70-200 f2.8 II and the original Kenko  1.4DGX and it will not focus with this combination. The camera just constantly hunts. The TC worked with my series I 70-200 but when I upgraded I also had to buy the Canon 1.4 II. The kenko works with all my other lens's and the quality is good. I have considered selling it but it fits my primes where the Canon won't.