MySQL 4.1 and up uses an authentication protocol based on a password hashing algorithm that is incompatible with that used by older clients,
you should do something like these:
mysql> UPDATE mysql.user SET Password = OLD_PASSWORD('newpwd')
-> WHERE Host = 'some_host' AND User = 'some_user';
mysql> FLUSH PRIVILEGES;
if you do these .the problem should resolved.try it!