Normally this means that your supplied password to access the database is not the correct one.

There is a difference between the admin user of your odoo environment (admin user) and the admin user of the database server (main password or database odoo password) . if you don't remember your initial password (created when you installed odoo), or you made a type in the during the intial installation, which prevent you now to backup the database. you can edit the odoo-server.conf (or openerp-server.conf) and include a new password. 

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refer this. already answered.

https://www.odoo.com/forum/help-1/question/recovering-master-password-73750

In the openerp-server.conf,you can find your password for admin after the addon_path (i.e) admin_passwd = admin...