After Multi-site install I get error logging in

I have gone through the multi-site network install (to an existing install on my server) and when I make the suggested changes to the wp-config file and the .htaccess file I can no longer log in to the /wp-admin. I get this error: “You do not have sufficient permissions to access this page”.

I am running the latest version of WordPress.

The weird thing is that it was working briefly for about 5 minutes and then kicked me out.

Any suggestions of what to look for?