Warning: mysql_connect(): Client does not support authentication protocol requested by server; consider upgrading MySQL client in /blah/somepage.php on line 123

The reason for this warning is because PHP4 can’t communicate with a MySQL5 server unless it’s using old passwords (set by using the OLD_PASSWORD() function below.)

There are two simple ways to fix this. The first would be to upgrade your version of php. Unless you *really* need php4 (or below?!) upgrade! I’m not sure php4 is supported any more and should be considered a security risk. If you can’t upgrade, just do this in your database:

update mysql.user set password=OLD_PASSWORD('thepassword') where user = 'theusername';
and:
flush privileges;

This should do the trick. Be warned, if you issue any GRANT statements after this you will have to update mysql.user again.