What does this->joints[i]->GetMaxForce(0) return?. I stumbled into this recently, and figured that the MaxForce needs to be set to a nonzero value, ie.
this->joints[i]->SetMaxForce(0, nonzero_val)

The odd thing was that I could do this->joints[i]->SetAngle(0, angle) with the MaxForce set to zero and it worked. AFAICT the joint was not static.