The following tables are taken from one of my subdomains which is a ravennuke.76 install. Don't worry if you don't have some of the tables such as nuke_nsnst_ as this fix should work for everyone experiencing permission based issues with phpbb not recognizing the admin value within your forum ACP:
...btw, I realize my above example already has me at user_level 2 but that is because I'm admin on that sub-domain
