Undefined value found in the stiffness matrix.

Hi I am Getting Following error when I am trying to solve Mosfet model in comsol

Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
.There are 9 equations giving NaN/Inf in the matrix rows for the variable mod1.phi0
. at coordinates: (1.85106e-007,-3.45295e-007), (7.68991e-008,-2.18897e-007), (1.31003e-007,-2.82096e-007), (8.2885e-009,-3.71345e-007), (9.66972e-008,-3.5832e-007), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns.

thanks and regards

Pavan Naik