Hello, Sometimes we may get the error on admin page once done with the Magento installation.
In that scenario, we have to do the following:
SET FOREIGN_KEY_CHECKS=0;
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';
SET FOREIGN_KEY_CHECKS=1;
