It looks like the MySQL driver he's using is too old for his MySQL server. He should try with the latest version for newer servers: http://softinnov.org/tmp/mysql-protocol-41.r I haven't made it official as it does not work for older servers IIRC, and I also never found the time to fully test it with more recent ones. But it should work correctly.
The problem could be this as well: http://dev.mysql.com/doc/refman/5.5/en/old-client.html
when you upgrade your mysql server from 4.x to 5.x the passwords in your "mysql" table for users stays old, which hashed a different algorithm.. so you cannot connect it using username/password anymore.
I think the link didn't work because I discovered it was a moderated thread.
Doc, what a lifesaver! I just spent the last 7 hours trying to figure out what was wrong with my remote rebol-based mysql app. It stopped working after I upgraded mysql. I spent most of my time messing around with mysql until I narrowed it down to the protocol. sql-protocol-41.r Addresses: User Error: ERROR 1251 : Client does not support authentication protocol requested by server; consider upgrading MySQL client (When using newer long hash passwords) and User Error: ERROR 1043 : Bad handshake (when using older short hash passwords) Thank you for posting this. I was getting to the point of panic.
Glad to hear that my driver helped you solve your issue. :-)