Error Opening Word Document with Custom XML

I created an XML file for a repetitive field (Client Full Name) within my word template but after implementing the custom XML and opening it I receive the following error:

HRESULT 0X80004005

Location: Part: /word/document.xml, Line:0, Column: 0

Here is the inside of the XML part:

<?xml version="1.0" encoding="utf-8" ?>

<mydoc xmlns="mydoc XML">

<Client_Full_Name></Client_Full_Name>

</mydoc>

Does anyone know how to properly save/package XML with a .dotx for templates? I can't use my template due to the error after using the fields from my Custom XML/XML Mapping Pane.