FPGA PID outputs NaN

Hello,

I'm working on a LabView project to drive DC motors from the FPGA part of a compactRIO 9063.

I've implemented a small VI to do so, based on optical encoders to retrieve the current motor axis positions and a PID to control the motor courses.

For some reasons I cannot explain, the PID outputs always send as NaN (as far as I can see using the indicator).

Any idea why I have such a behavior ?

Find below a snapshot of my VI.

thanks for your help,

Regards,

Christophe.