Regarding removal of singularity in the network

Hi all,

I am working on design and simulating a short distribution error. During execution , I came across an error which says , "There might 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 ). Can anyone tell me how to toubleshoot it and the reason of occurrence of such error?

Regards