Multiwii Tri yaw servo not moving

Hi,

I am having problems with my multiwii teensy tricopter.
I am using ITG3205 gyro, ADXL345 ACC and HMC5883 MAG. and a teensy as controller.
the problem is that the yaw servo doesn't move. all 3 motors work fine, just the yaw servo doesn't.
I have verified that the output is wired correctly by using a demo servo program.
I have used this pinout (http://www.multiwii.com/forum/download/file.php?id=1064&mode=view) with HWPWM6 and without allpins.

Does anyone know what the problem could be?

KoekieMonster