Question about contouring with cutcom

Dear community,

I'm trying with 3dexp to program a contouring with cutcom with a special curve : a spiral.
 

 

 

I have got a problem because the milling cutter wants only to do a turn : i think the milling cutter cannot penetrate the guide :


If i check the box "on curve" it is working (the milling cutter follows the entire drive curve)  but i can't choose now the CUTCOM option :



any idea to solve this problem ?

thank's to all