I have struck this a couple of times now so thought I’d put a reference here, if not for anyone else then at least for me!
Recent versions of MySQL 4 use passwords that are not compatible with PHP4. If you have received an error like this, you’ll know what I’m talking about…
Client does not support authentication protocol requested by server; consider upgrading MySQL client
To fix it, log into MySQL via the command line and use OLD_PASSWORD to change it so that’s it’s compatible.