Erro:"Derivative input 11 of 'teste_car​ol_convers​ortrifasic​o_13mar13/​powergui/E​quivalentM​odel1/Stat​e-Space' at time 0.44 is Inf or NaN. "

In my simulate block diagram when I modify the type variable-step for fixed-step happens this error message: "C' at time 0.000408 is Inf or NaN. Stopping simulation. There may be a singularity in the solution. If not, try reducing the step size (either by reducing the fixed step size or by tightening the error tolerances)."

I've tried to reduce the step size but it did not work and keeping return the same error message. And I don't know about the "singularity" that the error message suggests. How can I solve it? thanks