It sounds like you are attempting to back up a database while logged in as a reseller to someone else's cPanel account.
If this is the case, you have two options:
1. Login as the cPanel user directly then do the database backup
2. Create a .my.cnf file in that user's home directory with the username and password configured in that file. An internet search for .my.cnf will assist you with how to do this.
If you were logged in as the cPanel user and not as a reseller, please let me know.
Hmm, that's definitely something that needs looked at. I recommend you contact your hosting provider for assistance.
If you are the hosting provider (meaning you have root access to the server), you can have our technical analysts login to the server to diagnose and resolve this issue: http://tickets.cPanel.net/submit
Hmm, that's definitely something that needs looked at. I recommend you contact your hosting provider for assistance.
If you are the hosting provider (meaning you have root access to the server), you can have our technical analysts login to the server to diagnose and resolve this issue: http://tickets.cPanel.net/submit