It means the solver is trying to solve a non-linear system of equations but cannot find the solution.

Try these examples and you should realize why this happens. Sadly, the error-message is quite bad and does not provide all the information you need (it points to wrong equation-system)

loadString("

model M

  Real x,y;

equation

  x = sin(y);

  y = cos(x);

end M;

");

simulate(M);

loadString("

model M

  Real x,y;

equation

  x*time = sin(y);

  y = cos(x);

end M;

");

simulate(M);

Thank you for your reply. I had simulated these examples and has known that the first one had no start value, thus not calulated a solution. I'm trying to find out some error equation like that. Thank you very much.

You can try to use simulate(... , measureTime=true). It should at least list all non-linear systems and the variables that are part of them (if you did not find this out already).