If you have recently changed your username or password, you will need to update your dialer settings.

1. If necessary, disconnect, and make sure the MyStargate Dashboard is closed.
2. Double click the My Computer icon on the Desktop, then double click the Internet Connections folder
3. Right click the Stargate icon and select Properties.
4. Select the Account tab if it is not already selected
5. The User Name field should show your full name (This is how it appears when you send email)
6. Update the Account ID field with your new username if necessary in the format, username@stargate.net.
7. Enter your new password in the Password and Verify Password boxes.
8. Click Save. The next time you connect, it will use your new username and password.

Also, How do I change my email username and password?