Regeneration problem in Creo Simulate 2.0

Hi,

I have a problem in regenearting a model in Simulate 2.0 (structural):

in the main window, when I regenerate, the led on the bottom right remains always yellow and if I try to save the model, the message of warning "model has to be regenerated" and "mass properties not calculated" (or something like that, my creo is not in english), which are typical of when the model has the yellow led when you try to save it.

(while, instead, in the parametric the led is green without any problem).

Anyone knows what is it due to?

thanks