Simulation doesn't allow me to select a body from the body folder

Hi everybody

I have a simply problem that gets me stuck.

In the simulation section I am not allowed to select the whole body from the body folder but I can only select the external surfaces.

This creates interferences especially in the thermal analysis due to the parameters ( like temperature or heat power for example) are not applied to the entire model. I keep on clicking on the correspondant body on the body folder but there seems to be no way out.

What can I do to solve this problem?

Thank you for your help

best regards

Mario

SolidworksSimulation