Hi,

If you could do what you are attempting, it would produce an invalid XML document.

The element 'PT' is in the 'empty' namespace, the element 'DTS' is in the namespace 'http://www.aaa.org';.

You are trying to set the default namespace to 'http://www.aaa.org'; on the root element 'PT'.

In order for the XML to remain valid you would have to push 'PT' into the 'empty' namespace, something like this xmlns:e="", unfortunately XML does not allow this, you can't push things into the empty namespace. So by adding your default namespace you have effectively pushed 'PT' into the namespace 'http://www.aaa.org';, making the XML document invalid against the schema.

Now if you are trying to minimize the XML document a bit you could add an alias for 'http://www.aaa.org';

lxWriterSettings.NamespaceMap["aaa"] = "http://www.aaa.org";;

The XML would then look like this:

<PT xmlns:aaa="http://www.aaa.org"; name="tester1250">
    <aaa:DTS/>
    <aaa:DTS/>
    <aaa:DTS/>
</PT>

Note: The XML you have posted has other errors the prefix xsi is typically 'http://www.w3.org/2001/XMLSchema-instance'; you have it as xmlns:xsi="http://blah.org";, and as you have extra quotes in <DTS xmlns=""http://www.aaa.org">; I assume you have typed this rather than copied the output from Liquid objects? So the answer I have given is based on guessing your intentions to some extent.