"Invalid hexadecimal character reference" error parsing an XML with SAX processor

Hy to everyone

I have created a simple SAX parser for a very simple XML file.

When I run the code that follows I get this error:

"Invalid hexadecimal character reference"

The strange thing is If I change the "chunk size" for the data I send
to the parser, the error row changes. This behaviour is very strange!

I have done a one more test and I have set the chunkSize equals to the
file size and I have the same error at the end of the file.

The same XML file processed with another language doesn't raise any
error.

I use PHP 5.2.3 and a LAMP (AppServ Open Project - 2.5.9 for Windows)
on
a Windows VISTA PC.

The code I have used follows:

public function create_parser($filename)
{
   $this->fp = fopen($filename, 'r');
   $this->fsize = filesize($filename);
   $this->parser = xml_parser_create();
xml_set_element_handler($this->parser,
'Parser::start_element','Parser::end_element');
   xml_set_character_data_handler($this->parser, 'Parser::char_data');

}

public function parse()
{
    //$blockSize = 4*1024;
    $blockSize = $this->fsize;    echo 'Lunghezza file: '.$this-
>fsize;

    while ($data = fread($this->fp, $blockSize))
    {
        //$data = str_replace('\n','',$data);
        if (!xml_parse($this->parser, $data, feof($this->fp)))
        {
               echo 'Parser error: ('.xml_get_current_byte_index($this-
>parser).')

\''.xml_error_string($this->parser).'\' at line '.
               xml_get_current_line_number($this->parser). ' at col ' .
               xml_get_current_column_number($this->parser);
               return false;
         }
    }
    return true;

}

A piece of the XML following:

<?xml version="1.0" encoding="ISO-8859-1"?>
    <!DOCTYPE dblp SYSTEM "dblp.dtd">
    <dblp>
      <incollection mdate="2002-01-03"
key="books/acm/kim95/AnnevelinkACFHK95">
        <author>
Jurgen Annevelink
        </author>
        <author>
Rafiul Ahad
        </author>
        <author>
Amelia Carlson
        </author>
        <author>
Daniel H. Fishman
        </author>
        <author>
Michael L. Heytens
        </author>
        <author>

....

The Industrial Information Technology Handbook
        </booktitle>
        <url>
db/books/collections/IITHandbook2005.html#SeyfarthK05
        </url>
      </incollection>
</dblp>