The Computer Science and Engineering Dropbox uses the University's Active Directory Authentication Servers.
You should be using your University Network ID credentials for logging into this system.
If you feel you are using the correct credentials and you are still unable to login you need to reset your password.
You will need to go to my.sc.edu, scroll down to the "PERSONAL" section and select "View my IDs and manage my passwords"
Log in using your VIPID credentials since your network ID credentials are not working. Once logged in you can select your network ID and reset your password.