Now you are talking about computer simulation problems.
Just an artifact of how the program is computing things. Division by zero, too quick rate of change for compution step size, etc. are some examples why a simulation program aborts a run.
A good deal of electronic engineers time is spend debugging simulation programs to find out why it is aborting run.
Sometimes just puting in a small value resistor or small capacitor somewhere in the circuit fixes it.
MOSFET circuits are notorious for having simulation difficulties.