admin cp not recognizing login

[rhiecakes]

this happens to me a lot. the admin cp won't recognize me at all, after logging into both my site, and the CP itself. it gives me this error:
"An error has occurred.
You do not have permission to access Admin Control Panel."
even after logging into my site, refreshing, logging out and back in, or changing my password and logging out/in again.
sometimes it lets me log in, most of the time, it does not. i don't know if it has something to do with cookies or caching, but it is very frustrating. i'm on chrome and i have cookies enabled so i can't understand why it keeps doing this.