The error message in Joomla when the username/password don't match are: Warning | Username and password do not match or you do not have an account yet.
Your error seems to be related to the frontend, and the corresponding administrator section error would be:
You do not have access to the Administrator section of this site.
This is all caused during the "authorization" process after you login. Basically "authentication" completes successfully (in other words your username and password are correct) then the code looks to see what you're allowed, or authorized, to access.
The error is triggered here:
Line: (approx 198-207)
// Check the user can login.
$result = $instance->authorise($options['action']);
What you need to do is either reinstall your site, or look up issues with the ACL tables. I would recommend reinstalling.