>Thank you Sergey. I'm sorry for being totally ignorant of how this all works. I copy and pasted "what I'm told is the XSD" into RAD.xsd. (see in attached zip file) How do I proceed? I've placed the file in the same directory.
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The XML schema you posted is invalid. You have to get correct one. After that you can reference it using XA XMLSchemaLocation property.

Keep in mind that The XA can process complex XML but not all of them. Your XML could be to complex for XA to process.