How to solve non linear problem and how to converge it .

I am using COMSOL 3.5a. I am solving heat transfer through conduction and then convection. During the first stage of conduction the model is not converge it shows the singular matrix error.

My question is how to change a non linear solver setting? so that the model is fully converged.

Any idea is highly appreciated.

Thanks in advanced.

Vinay Patel