Asynchronous Machine time dependent startup, singularity error

Hello,

I am trying to simulate a ASM in the rotating machines physics, time dependent.
The Stator slots are coupled to the electrical circuit physics for a Voltage excitation
The rotor slots are also coupled there to define the short circuit resistants.
I am using the ODE Interface for a rotation velocity equation.

When simulating for 20ms, with a timestep of 1ms(or less), everything is fine (rotor slowly starts rotating).
But when I want to calculate for a longer time, the computation stops somewhen in the middle, saying something like:

"Repeated error test failures. May have reached a singularity.
Last time step is not converged."

I choose the mesh as extremely fine and tried a step size of 55us.
As "Maximum Step" and "Initial Step" I'm using the same value as for "Step Size".
But it does not help...

Does anybody have any advice?

Thanks in advance