it doesn't work depends on thickness of electrolyte

Hi,

I am trying to make the modelling to predict potential distribution under the thin electrolyte. My model consists of 2 electrodes covered with thin electrolyte.

When the thickness of electrolyte was 1mm, computation was successful and I obtained reasonable result. But, when the thickness is thin (0.02mm), it doesn't work. Boundary conditions are totally same. Only difference between them is thickness of electrolyte. I don't know what problem this model has.
I would appreciate if someone gives me some advice about it. I attached 2 files above 2 examples.