Recently I started noticing exceptions in my log files that stated "hexadecimal value 0x1A, is an invalid character". I did some searching and a lot of other people have had the same problem. It occurs when someone pastes in text that contains specific unicode characters that are invalid in XML. From what I gather this frequently happens when someone copies in text from Microsoft Word.

The trick was to find out which characters are invalid and then use a regular expression to remove them.

You can look at the specs for all the details:

• http://www.w3.org/TR/xml11/#charsets
• http://www.w3.org/TR/REC-xml/#charsets
• http://www.unicode.org/Public/UNIDATA/UCD.html

But it is probably easier to just get the code:

        /// <summary>
        /// This removes characters that are invalid for xml encoding
        /// </summary>
        /// <param name="text">Text to be encoded.</param>
        /// <returns>Text with invalid xml characters removed.</returns>
        public static string CleanInvalidXmlChars(string text)
        {
            // From xml spec valid chars:
            // #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]    
            // any Unicode character, excluding the surrogate blocks, FFFE, and FFFF.
            string re = @"[^\x09\x0A\x0D\x20-\xD7FF\xE000-\xFFFD\x10000-x10FFFF]";
            return Regex.Replace(text, re, "");
        }