The XML expansion pack is invalid.
Debugging smart documents in Office 2003? Love <snicker> the debug-time feedback that Excel and Word give you when something is not quite right? Have no idea what the cryptic error messages really mean? You are not alone...
Here is a MSDN article written by the wonderful Siew Moi Khor and Octavian Timofte, one of the product team members, that will help you debunk some of the mysteries of smart document development.