Invalid XML messages can be deciphered by testing the XML file with an XML validator.  There is a free validator online at 

http://www.stg.brown.edu/pub/xmlvalid/

The validator tool may help pinpoint a problem in the XML file; thus, helping you determine what is needed to generate a valid XML file.  Follow the on-screen instructions to upload your XML for testing

A typical invalid XML message in sTToXML may read as:

759. XML Failure. The uploaded XML file is invalid according to the smbxml .dtd specifications.
Error Reason: 'Element content is invalid according to the DTD/Schema....