Encounter an error when simulating GaN HEMT electrostatic simulation

Dear All, I am new to COMSOL simulation environment.At present, I am facing issue when doing electrostatic simulation of GaN HEMT.Following are the error message getting during computation of electrostatic simulation.

• Feature: Stationary Solver 1 (sol1/s1) Undefined value found.

  • Detail: Undefined value found in the equation residual vector. There are 1465 degrees of freedom giving NaN/Inf in the vector for the variable comp1.faio. at coordinates: (1.85429e-005,1.73333e-007), (1.85429e-005,1.8e-007), (1.85429e-005,1.86667e-007), (1.85429e-005,1.93333e-007), (1.85429e-005,2e-007), ...

  Kindly help me to sort out the issue.

  Regards Srikant.