Copy the content of attached file and try to save it :

content: Unable to transform rich text: Exception during processing of cocoon://_plugins/cms/convert/html2docbook [...]

Caused by: org.xml.sax.SAXException: Fatal error parsing null (line 8 col. 4): An invalid XML character (Unicode: 0x1) was found in the element content of the document.
org.xml.sax.SAXParseException; lineNumber: 8; columnNumber: 4; An invalid XML character (Unicode: 0x1) was found in the element content of the document.