Accuracy of magnetometer always 0

I now have de motion library 6.1 fully working with the MPU-9250 on a NXP LPC-4078. Strange thing that happens is that I never (accept once) got a fix with the magnetometer. The accuracy level is always 0. Could the setup of the rotation matrix be the problem? (never touched it)

I'm using SPI for communication and it was quite a pain to get the communication with the compass running. I won't exclude an error there.

Thanks in advance