Surface to surface radiation problem

Hi everybody,

I attach a (simple) test case which is giving me problems. It is a 2D axisymmetric problem, with a coil and a screen. The coil is modeled using a heat source, and there is radiative heat transfer to the screen and ambient. When the power assigned to the heat source exceeds a given value (about 800 W), the solver crashes with the message: "Undefined value found. - Detail: NaN or Inf found when solving linear system using PARDISO."

I am using version 4.3a of the software. Anybody please help? Thank you.

Alessandro