Simulation Error

Hi there. I am working on effect of AC electrical field on the microelectrode.

However, when I tried to compute the study (either by using stationary or frequency domain), I kept getting error message such as below:

#Internal error: cannot convert ElemStruct to int.
-Value:d7
Error in multiphysics compilation.
-Feature: Compile Equations: Stationary (sol2/st1)
-Error: Internal error: cannot convert ElemStruct to int.

Can anyone help in this? Thanks