The Formula of Windows Vista
This phenomenon is the formula of Windows Vista.
Please refer to the following contents for further information.
In Windows Vista, if you are unable to use Dial Up to connect to the Internet under the circumstances of using Guest Account to log on.
Please use user accounts under Administrator and Standard Account to log on when using Dial Up to connect to the Internet.
[Windows Vista]About Guest Accounts
[Windows Vista] About types and authorities of user accounts.