Command button update atribute

I have an xhtml with a p:commandButton update="tbResult" and a table id="tbResult", so when i click the button it should (in theory) update the table... but i have and error telling me this:

Cannot find component for expression "tbResult" referenced from "formprueba:btnIn".

The weird thing is that i have a panel, and a p:messages and their ids are recognized by the attribute update in the button... why does the <table> id is not recognized?

so in small words this works:

update="panel, growl"

this does not (gives error mentioned earlier):

update="panel, growl, tbResult"

btw, everything is inside and <h:form id="formprueba">

hope you can help...