You should still be able to reach the admin area. My personal setup is for phpBB 2.0.18 so I can't say for 100% whether a 2.0.19 version is the issue... But this should not be a common issue...
When you talk about the mod... are you referring to the sessions.php mod listed in the README document? or a MOD for changing the registration or profile buttons? Assuming it is the sessions.php file you can PM me the text of that file and I will peek at it.
Also, for further follow-up, do you have access to the database tables via phpMyAdmin (or similar) If you do you can verify (or change) the 'user_level' field for that particular user in the 'phpbb_users' table... it should be set to 1 for administrators...
Hope this helps,
Greg
CB3PD Developer - CB Connector (formerly phpBB Connector) plugin