Problem in thermal stress modelling

Sir,

I am working on thermal stress modelling on EDM process using COMSOL 4.0a. I am using heat flux as a input.

At some places I am getting negative Surface Temperature which gives me wrong results of stresses. I have tried in many ways to solve it. When I apply very fine meshing it gives errors. And I also found that as I change mesh size negative temperature also changes.

Is this problem related to mesh size only or any thing other???

Thank You

Sagar