Changed DB prefix, now can’t login, whoops…

So I changed the DB prefix in my wp-config.php, then renamed each of my tables.

Now for some reason I can’t log into the admin area, I’m met with ‘You do not have sufficient permissions to access this page.’ once I enter my details.

I guess that this has something to do with the rename, but I can’t think what. can anybody suggest how I can fix this, short of renaming everything back?

Thanks!