The parser will fail a file if it doesn't conform to the rules specified in the DTD file. The error email will have the error message returned by the parser complete with the line number and line position of the error.
The parser will also fail if exotic ASCII characters (ie those with a character value of greater than 127) are not coded (sometimes referred to as escaping).
On the MS platform a method such as Server.HTMLEncode(string) will do this.
An alternative is to leave the characters as they are and specify an 8 bit encoding scheme e.g.
<?xml version="1.0" encoding= "iso-8859-1" ? >
For more information seehttp://www.w3.org/TR/html401/sgml/entities.html also MSDN article Q238833.