When I ran the update.php, it asked me for my username/password. It never did that before?
update.php had security added to require native admin id/pwd to enable to run... A workaround is in doc in case you no longer remember the native admin credentials.
In your MySQL database, go to the config table, find bridge_enable and set it to '0'.
You can also go to bridgemgr.php.. It will prompt for native cpg admin credentials and will disable the bridge.
I did so, now I can logon as a standalone admin, but once I enable bridging, my admin user does not get admin priveledges in Coppermine - although it DOES have them in phpBB3?
Are you using cpg groups or those from phpbb3? (guessing phpbb3...)
Turn on debug for all users, http://documentation.coppermine-gallery.net/en/errors.htm#errors_debug_mode_config
give instructions from config - followed by manually via phpMyAdmin.
Once logged in, 'show' debug data (option at bottom of every page when on)
See what is specified under "User Data" - specifically the list of groups assigned, "has_admin_access", and "group_name".
Post results here...
Also, the "pre-bridged" admin user id is NOT allowed to logon...
once bridged, the native cpg admin is only usable for special tasks like update.PHP and unbridging.
Let us know what you find...