That's because the login link you were using is probably

domainname.agentfire.com/wp-admin/

When your site goes live, you lose the '.agentfire' part, so the login link would be

domainname.com/wp-admin/

When in doubt, you can always just go to the bottom of your website and look for the 'admin' link on the bottom of your website. Clicking that will bring you to the login page.

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