PID Tuning Error in Simulink - 'Cell contents reference from a non-cell array object.'

My question is does anyone know what could be causing this error when I auto tune the PID block in Simulink?

Message - Linearization error; source - unknown; Reported by - Simulink Control Design; Summary - Cell contents reference from a non-cell array object.

I have developed a closed loop feedback model in Simulink for a second order system (a force balance containing a LVDT and a Voice coil actuator). My issue is that when I try and use the tune functionality of the PID controller block I get the error above.

I have simplified the model down to a very basic system as seen below and still get the same error. I can tune manually by using the Ziegler Nichols Method however I would rather be able to tune using the Simulink functionality.

Any steps or advice on how to debug this issue would be very appreciated.

Thanks,

Darren

[Arkadiy Turevskiy]

Is there any way you could attach this simple model? When I create a model just like shown in the image, everything works just fine, as expected. Are you using any variables to parameterize step block or PID controller?