I have upgraded the PHP version to 5.3.3 ( non thread safe VC6 compiled ) and the problem still exists.

I have upgraded the PHP version to 5.3.3 ( non thread safe VC6 compiled ) AND RESTRTED ECLIPSE ;P and the problem gone. It works now.
so maybe php 5.3.1 and xdebug 2.1.0 doesn't mix together well.

If you use binary indexes in arrays, xdebug want show variables
Example:
<?php
$index = chr(0);
$x = array( $index => 1, 2, 3 );
var_dump($x);
?>

Maybe this bug helps

same here with php 5.3.3 + xdebug 2.1.0 under ubuntu 9.10 in different eclipse & aptana versions

Closing this as it works for the original reporter.

@fratilkus: There is already another report for that: http://bugs.xdebug.org/view.php?id=650

@dasjo: Talk on the mailinglist, and provide there remote debug log from a small reproducable script. For a debug log, see: http://xdebug.org/docs/remote#remote_log