My provider recently upgraded to Debian Sarge and MySQL 4.1 which promptly broke my Wikipedia setup as below leading me to wild goose chase to http://dev.mysql.com/doc/mysql/en/old-client.html.
Client does not support authentication protocol requested
by server; consider upgrading MySQL client
The easy fix is to just change the mysql wikiuser password using the mysqladmin command as below:
mysqladmin -u <wiki-user> -p password <new-pass>