An error occurred while parsing EntityName. Line1, position 844

Just replace them:

Not valid in XML elements:

"   "
'   '
<   &lt;
>   &gt;
&   &amp;

  public static string UnescapeXMLValue(string xmlString)
  {
    if (xmlString == null)
        throw new ArgumentNullException("xmlString")
    
    return xmlString.Replace("&apos;", "'").Replace("&quot;", "\"").Replace("&gt;", ">").Replace("&lt;", "<").Replace("&amp;", "&");
  }
 
 public static string EscapeXMLValue(string xmlString)
  {

    if (xmlString == null)
        throw new ArgumentNullException("xmlString")

    return xmlString.Replace( "&","&amp;").Replace("'","&apos;").Replace( "\"", "&quot;").Replace(">","&gt;").Replace( "<","&lt;");
  }