Simulate simple eddy current brake

Hi all,

I am very new to Flux and just acquired the student licence to try and parametrically develop a simple eddy current brake using permanent magnets.

For now, I have created a rotating disk and a fixed, simple magnet and am trying to get the resulting torque created around the center axis of my disk. 
However, as soon as I add sensors to read out the data that I think is necessary, I get hit with a "The region [...] is in contact with the sliding zone." and I can't figure out what I'm doing wrong.

All help is greatly appreciated, and please have mercy with a newby asking stupid questions.

Cheers,

Tom