error while running simulation!!!

Im getting following error while running a control system simulation 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) What should I do?

[Torsten]

First you should look at the results up to the time when the solver stops and see whether they are reasonable. Usually, such an error message indicates that the solution gets unphysical.

Best wishes

Torsten.

[M Gokul]

thank you very much