singularity error

Hi,

I am trying to solve a time dependent, 2D, multiphysics problem using "Transport of Diluted Species" and "Electric Current". In my model there are basically 5 domains in series: at all of them and at every time there are always diffusion, electromigration and one reaction (R1) taking place. At the second and the forth domain, there is an additional reaction(R2) that is taking place periodically. My boundary condition is no flux for any species at the surrounding walls.

When I try to solve the problem, I am getting the error:
Repeated error test failures. May have reached a singularity.
Last time step is not converged.
-Feature: Time-Dependent Solver1 (sol1/t1)
-Error: Repeated error test failures. May have reached a singularity

If I decrease the reaction rate for R2 by 10^(-6), the program runs without a problem and gives me a reasonable result. Nevertheless, these values are not real, and I need to change the parameters back to the original ones.

I read at other threads that the boundary conditions might be causing the problem. I tried to use "flux discontinuouty" at the interfaces between the domains, but without success.

Has anybody else had a similar problem? Can you please help?

Thank you in advance,
Nancy