validation error in the us-phone component in a template

I'm using the "us-phone.xbl" component example in a template (library) and it's giving to me the following error when I enter an invalid phone:
"An empty sequence is not allowed as the second argument of resolve-QName()"
When I use the component outsite the template it works fine. Could anybody help me to adress this error?

The code that is giving the error in the us-phone component is:
<xf:setvalue if="not($is-valid-phone-string)" ref="$binding" value="if ($phone-string = '') then '' else 'INVALID_NUMBER'"/>
when I remove the not(...) function it don't give an error. Could it be this function that is giving the error?
Following the code I found that the javascript file that is giving the error is:
\ops\yui\connection\connection-min.js
And the function is:
B.handleTransactionResponse(C,D)

Thanks