Error on the install page:
ERROR: mysqlnd cannot connect to MySQL 4.1+ using old authentication
SHOW VARIABLES LIKE 'old_passwords' (returns TRUE)
It's a MySQL configuration issue: http://dev.mysql.com/doc/refman/5.1/en/old-client.html
When I resolve it I will edit this post with the workaround/fix.
[EDIT]
Not informative regarding the MySQL configuration I had assumed was the cause, but I changed PHP version and the error is gone.
5.2.13 (no error)
5.3.2 (error)
Note: Both CGI versions