Admin Permissions Gone – database problem?

Externally, my site is functioning properly. All posts are in and it can be browsed correctly.

However I now have a new problem. When I try to login it accept my username and password but takes me to a message which says:

“You do not have sufficient permissions to access this page.”

I think this is a simple error in the database which can be corrected by editing a field somewhere.

If possible, I am happy to create a new user and then upgrade that user to have administrator privileges. I have searched the Codex and the forums but cannot seem to find an answer. Some had success forcing a db upgrade but I do not think the file structure is the same anymore.

Thanks