Calcblend failed

[Winniethepooh]

Hello, I have a problem with the compilation of a custom model of NPC using a custom rig and custom animations.

I've started my qc from the hl2_sdk's qc used for the civilian, I have updated them to match with my bone names. When I run the compilation, I get the message calcblend failed in head_rot_x.
The calcblend is done in the body_poses_lean.qci by the following line :
$sequence head_rot_x { a_head_rot_lt a_head_rot a_head_rot_rt calcblend head_roll "eyes" XR } delta autoplay hidden

If I delete it, my compile runs fine and my model is working, except that I haven't the head roll, of course, because I have deleted it.
Does anyone know what could be the problem? Every other calcblend are ok, so it sounds mad for me.