xpath query failing

I am trying to chase down an issue with the Microsoft WIX msi
installation framework. I have some xml such as:

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      throwExceptions="true">
    <!-- ... -->
</nlog>

The selector I am using is "/nlog/@throwExceptions" which is failing and
it appears to be as a result of the default namespace specifier for
"http://www.nlog-project.org/schemas/NLog.xsd".

I am not clear on how this invalid, but it looks to be more of a restriction
on the parser? Am I overlooking an issue with the actual xml format is
it related just the parser?

Thanks,
jlc