Nonlinear iteration convergence error in Simulink?

Hi,

I am simulating a chemical reactor feedback control model in Simulink, which involves algebraic loops and s-function to model the reactor's dynamic model. I got the following error:

"An error occurred while running the simulation and the simulation was terminated Nonlinear iteration is not converging with step size reduced to hmin (4.1242630063704837E-14) at time 11.608768336667561. Try reducing the minimum step size and/or relax the relative error tolerance"

I am not sure this error was caused by the high stiffness of the ode system that I am trying to solve, or by the algebraic loop issue. Since, I read that a iteration method is used to solve the algebraic loop.

The ode system have six states, and at the time when the simulation was determined, the derivative of one state reached 9*1.0e+07, while the other derivatives are very small values compared with this one.

Thanks!

Zixi