Error 404 not found magento admin login page which is the general error when upgrading from one server .When you transferred your magento installation from one server to another. Now, If you cannot login to admin panel and If go to the admin login URL , If you are getting the following error message:-
“Error: 404 Not Found”
Some of my module’s pages also show this error.
So check the below details for you solution.
If log is enabled then go to var/log directory and check what is the actual error and check whether are getting below errors ? Error 404 not found magento admin login page is common one when you are upgrading from one server.
Recoverable Error: Argument 1 passed to Mage_Core_Model_Store::setWebsite() must be an instance of Mage_Core_Model_Website, null given, called in YOUR_PATH\app\code\core\Mage\Core\Model\App.php on line 555 and defined in YOUR_PATH\app\code\core\Mage\Core\Model\Store.php on line 285
Recoverable Error: Argument 1 passed to Mage_Core_Model_Store_Group::setWebsite() must be an instance of Mage_Core_Model_Website, null given, called in YOUR_PATH\app\code\core\Mage\Core\Model\App.php on line 575 and defined in YOUR_PATH\app\code\core\Mage\Core\Model\Store\Group.php on line 227
The reason for this error is that store_id and website_id for admin should be set to 0 (zero). But, when you import database to new server, somehow these values are not set to 0.
So for that Open PhpMyAdmin and run the following query in your database:-
UPDATE `core_store` SET store_id = 0 WHERE code='admin';
UPDATE `core_store_group` SET group_id = 0 WHERE name='Default';
UPDATE `core_website` SET website_id = 0 WHERE code='admin';
UPDATE `customer_group` SET customer_group_id = 0 WHERE customer_group_code='NOT LOGGED IN';
Also you can do this by another method that just go to app/etc directory and check if is there any file named as use_cache.ser if yes then delete that one.Then yoou problem is solved now.