A validation error occurred when validating the instance document
If this error occurred in a script section of your document, you should probably read this FAQ entry.You have used a character that is not considered a "name character" in an attribute value.The document does not look like HTML, therefore automatic fallback could not be performed, and the document was only checked against basic markup syntax.
The document type could not be determined, because the document had no correct DOCTYPE declaration.
Check that you are using a proper syntax for your comments, e.g: .
This error may appear if you forget the last "--" to close one comment, therefore including the rest of the content in your comment.
One common cause for this error is the use of XHTML syntax in HTML documents.
Due to HTML's rules of implicitly closed elements, this error can create cascading effects.