At the time I was writing the question I founded a soution! So I answering my own question.
In your string.xml please don't use a space char like
<string name=" setting_notification"> ...
instead of
<string name="setting_notification"> ...
The xml parser will prompt any error messages and your R will be generated with the sintax error!
Im my case I didn't see soon the problem, becuse all my strings are automatically generated from a URL, where all my strings are.