Or something like this. I didn't write the right code, but that's the idea.

Thanks for all

Bufff... now works on debug configuration, but if I switch to realease, another error appears
(I will try to translate from spanish):

The symbol (token) StartElement in the state EndRootElement will result in an invalid XML document.
Be sure that ConformanceLevel is defined like ConformanceLevel.Fragment o ConformanceLevel.Auto if
you want to write an XML fragment.

I tried the two ConformanceLevel but doesn't work.