Yahoo have many options to retrieve the forgotten password. People are careless while creating an account and then suffer later. Some of the options available at yahoo are :
(a) Give your mobile number, so that when you forget they will text you.
(b) Give an alternative e-mail ID, so that whenever you forget your password, a mail will be send to that other mail ID given by you.
(c) Security questions. Yahoo normally asks you to answer two different security questions. You have the freedom to chose or to create your own security question. Always give a remember-able question and answer.
Normally this message is shown when you do not remember your password, have crossed the maximum number of login attempts a day, forgot the security question or answer and you have not given the option of alternative mail ID an d phone number. Therefore be careful and write it down anywhere as soon as you create an account or change your settings.
As you have already received such a message, either you can re-think about your password and try attempting it after 24 hours or try to recollect the security questions and answers. If nothing works, you will have to contact yahoo customer service or give up the account. As you are insisting that you have been using the correct username and password, then try clicking on forgot password link and enter the security answers for the security questions. If you have given your alternative mail ID or Phone number, chose the option to send you a password recovery information.
"Do not give up, things might not favour you always"