Did you change the password for that other mail account? If so, did you also update your Yahoo! Mail account? Yahoo! Mail doesn’t know if you have a new password unless you enter it. So, editing this information in your Yahoo! Mail account settings should correct the problem. And it’s simple!
To do it:
Note: If you update this setting and still have trouble, contact your Internet Service Provider or your work or school’s Network Administrator to see if too many password attempts tripped a switch that temporarily blocks your account.