During an update from 2.3.1 to 2.5, I received this database error while running the installer.
A database error occurred
Error Number: 1060
Duplicate column name ‘can_search’
ALTER TABLE exp_member_groups ADD COLUMN can_search char(1) NOT NULL default ‘n’
Filename: updates/ud_009.php
Line number: 112
After this error, I dropped all the tables from this DB then imported from my backup. I also checked all the permissions according to the “troubleshooting upgrade error” article. Now when I run the installer I do not receive an error but it just returns the 404 page.