Importing 3DS Max CAT rig as humanoid for mecanim.

I'm having problems with importing a rig as humanoid. The rig has the correct bone structure, and it seems to import OK, but no animation plays in game (the model floats around in a t- pose). The animation plays ok when I import the rig as "Generic" type, but since I want to use IK, this isn't an option.

I've heard that there are problems when exporting from CAT, can anyone help by giving me an idea of how I should rig my models in CAT for export as a humanoid compatible with Unity?