PHP XML Error

Hello,

I am trying to read XML file and store in sql table. I got two errors.

PHP Warning:  XMLReader::open(): Unable to open source data

Warning: XMLReader::read(): Load Data before trying to read

How to solve it ?

THANKS IN ADVANCED.

$reader = new XMLReader;
$reader->open('filename.xml');
while($reader->read())
{
    ///
 }