The output method is set to HTML, but the result contains one of the control characters #x7F-#x9F. These characters are allowed in XML, but not HTML. The most likely cause of this error is that the encoding of your input document is incorrectly declared. Microsoft Windows uses codes in this range to represent special characters such as an em dash or a euro currency symbol. If your source XML document uses these Microsoft codes, it must declare this by specifying encoding="cp1252" in the XML declaration. Otherwise they will be taken to represent the Unicode control characters at these positions, which are not allowed in HTML.