Admin password is not recognized in my daughters acct

Ive set up an accouont for my daughter and have set the parental controlls for the account. When we try to download a game or make any change she is prompted to enter an Admin username and password. This is where the problem is. I enter my username and password (it is the same form day one and has never been changed and I can actively use it to make changes when logged into my user/admin user.)and it will not accept it and will not allow me to make changes to her acct.

please help before i throw this computer out the window!