Error message: The name 'flowthru' is invalid

Good morning,

I am trying to save an XML spreasheet as an interactive website, but I am
getting an error message that states "The Microsoft Office Spreasheet
Component could not load the XML data. The name 'flowthru' is invalid"

Does anyone know what may be causing this? There is nothing published on
MSDN support, general microsoft support, or application level support.

Thank you,

Dan