pem used in system idenfication

I am new in matlab.when pem used in system idenfication,it always causes the following error.

    ??? Error using ==> idminimizer at 112
  The loss function cannot be computed. The initial model may be unstable.

Error in ==> idestimatorpack.idminimizer.minimize at 20
[xnew, resnorm, residual, exitflag, output] = ...

Error in ==> idss.pem at 449
OptimInfo = minimize(Estimator);

Error in ==> iden_tool at 62
m=pem(data,m);

can you help me.thanks.

[Rajiv Singh]

That can happen if, as the error message suggests, the starting model is unstable. To go further than that, you will have to post some more details. How do you configure m? What kind of data are you using?

[Gergely Takács]

Rajiv,

Does this mean that pem() can only handle stable models?