coupling electromechanics with electrical circuitry

Hi,
can some one help me please?
I want to couple electromechanics with el. circuit to solve cantilever problems.
And the problem is, I applied a button surface as a terminal for el. circuit and this surface I also need for thin-film damping. But I can't apply this surface in thin film properties (not applicable).
I tried allredy to delete a terminal, because I thought I can't apply one surface in several interfaces. But no change.

Thanks