in a patch (i think is a mertro object) always says
error: message stack overflow
can anyone tell me what's the problem?

post your patch.
The meaning of this message is that There is an infinite loop of information.

you'll get these all the time. it's probably the single most common error.

as giair says....some information in your patch is feeding back into itself. if you are using a simple [ f ] x [ + 1 ] counter, make sure your patch cords are connected to exactly the right inlets, same as in the documents.

you also get that error when you make a patch that generates an array that's too big....or a patch that generates infinite objects.