WARNING: An Error occurred, please refresh the page and try again.

I was upgrading a 1.5.1 install to 1.5.4
Imported the DB
Did the DB upgrade fine

Store page displays this text at the bottom

WARNING: An Error occurred, please refresh the page and try again.

Trying to access the admin area I get this

WARNING: An Error occurred, please refresh the page and try again.
The resulting debug file contents are
[14-Mar-2016 21:18:35 America/Chicago] PHP Fatal error: 1062:Duplicate entry '0' for key 'PRIMARY' :: insert into admin_activity_log (access_date, admin_id, page_accessed, page_parameters, ip_address, gzpost, flagged, attention, severity, logmessage) values (now(), '0', 'login.php ', 'camefrom=index.php', 'my_ip_address', '‹Ž\0', '0', '', 'info', 'Accessed page [login.php]') ==> (as called by) /home/kobrawd/public_html/demo154/mt_admin/includes/functions/database.php on line 53 <== in /home/kobrawd/public_html/demo154/includes/classes/db/mysql/query_factory.php on line 155

Php V = 5.5.31
mysql = 5.5.48

In a normal configuration, the admin_activity_log table has its primary key set to be the log_id field, which is an auto-incrementing integer field.
It seems yours is not properly set to be auto-incrementing, for whatever reason.

DrByte,
Thank You
I ran this and can now access

ALTER TABLE admin_activity_log CHANGE COLUMN   log_id  log_id int(15) NOT NULL auto_increment;

My bad. I should have said big-integer field.

The upgrade SQL (since v150) is:

ALTER TABLE admin_activity_log CHANGE COLUMN log_id log_id bigint(15) NOT NULL auto_increment;