Citizen Hand CAT Rig problems

I’m having a odd issue using the Citizen hands rig I got from here http://source.maxofs2d.net/gmod/3DS2011_CAT_c_arms_citizen.max

I can’t link any type of constraint with it, for example I want to animate a shotgun but I want to the IK Target to move when the model moves, I’d simply link a constrait from the IK controller to the model but this is impossible as any attempt at doing it results in “Link Constraint Not Completed”

Here is a picture
https://dl.dropboxusercontent.com/u/52828637/Problem%20(2).png