I've got a little further with this....
Created the missing table using the following SQL:
CREATE TABLE `phpbb_sessions_keys` ( `key_id` varchar(32) NOT NULL default '0', `user_id` mediumint(8) NOT NULL default '0', `last_ip` varchar(8) NOT NULL default '0', `last_login` int(11) NOT NULL default '0', PRIMARY KEY (`key_id`,`user_id`), KEY `last_login` (`last_login`) ) TYPE=MyISAM;
Next I deleted and recreated the phpbb_sessions table as that had some fields missing from it (namely session_admin).
CREATE TABLE phpbb_sessions ( session_id varchar(32) NOT NULL default '', session_user_id mediumint(8) NOT NULL default '0', session_start int(11) NOT NULL default '0', session_time int(11) NOT NULL default '0', session_ip varchar(8) NOT NULL default '0', session_page int(11) NOT NULL default '0', session_logged_in tinyint(1) NOT NULL default '0', session_robot varchar(32) default NULL, session_admin tinyint(2) DEFAULT '0' NOT NULL, PRIMARY KEY (session_id), KEY session_user_id (session_user_id), KEY session_id_ip_user_id (session_id,session_ip,session_user_id)) TYPE=MyISAM;
Now when I run the db_update1.php script I get redirected to the login screen. Whey I try to login I get an "Error in obtaining userdata" message. Namely:
SQL Error : 1054 Unknown column 'user_activate_date' in 'field list'
Any suggestions?