They think it's the complex conjugate terms in Eq 9 and 10 which is bad. I think Bianch et al tried to fix this. http://arxiv.org/abs/1004.4550
But the new spin foams have a divergent physical inner product, so that's another problem. Group field theory renormalization?
But if the theory is renormalized, how can it have a fundamental scale of discreteness?