Sometimes, unreadable characters are introduced into the XML file exported from SPSS for some regression models (PMML element GeneralRegression).
This happens usually when the PMML tag on the top of the file refers to http://xml.spss.com/spss/spss-logreg instead of http://www.dmg.org/PMML-3_1.
Whenever a file containing unreadable character is uploaded to the PMML Converter, an error will be produced with the following message: "This is not an xml file". In cases like this, we suggest you locate where any unreadable characters may be located and delete them before conversion. If you have more specific information about this problem, please let us know.