HP Color LaserJet 2605dn vertical stripe when printing

Hello,

I would like to solve my printing problem, so I hope somebody can help me!

 When printing a page I get a vertical stripe (color is blue).

When I open the front door, I see that the transfer belt has inkt on it, when I close the frontdoor, the printer starts with the Initializing proces. When I open the door again, the transfer belt is clean.

But when I print a demo page, the transfer belt is not clean any more (inkt).

I think the blue toner is broken, is that correct? Or is it something else?

Kind regards,
Martin.