Object reference not set to an instance of an object

[svidille]

Dear Dan and deal all,

Simone once more. I opened the sample "Dynamic Simulation - Water Tank Level Control.dwxmz" from the sample library. When I run it (without doing anything), I´m getting this error at minute 03:45. It happens when I run the simulation many times one after other.

Could you point to me what I am doing wrong?

Dynamic Simulation - Water Tank Level Control-copia.zip

Thanks,
Simone