Magento - 404 Error

How to find Error in Magento 1.7.2:


1. Enable the Developer Mode :

            Go to Index.php


1. Enable The Developer Mode:

Now the error may be like this:

simplexml_load_string() [function.simplexml-load-string]:

 Entity: line 1: 

parser error : 

XML declaration allowed only at the start of the document 

in C:\wamp\www\{MY PROJ}\app\code\core\Mage\Core\Model\Layout\Update.php on line 445

2. Enable the Log in index.php:

Mage::log(print_r($filename, true));

find Last error in /var/cache/system.log

That's it!