You purchased an upgrade license and key for Windows Vista. When you start from the DVD and then try to install Windows Vista by using this upgrade key, you will be blocked from continuing.
This problem occurs because Windows Vista does not check upgrade compliance. Therefore, you cannot use an upgrade key to perform a clean installation of Windows Vista.
To resolve this problem, use one of the following methods.
Start the installation from a compliant version of Windows, such as Windows Vista, Microsoft Windows XP, or Microsoft Windows 2000. After you have started the installation, you can select Custom at the installation choice screen to perform a clean installation.
Purchase a Full Product License. This license will let the installation continue after you start from the Windows Vista DVD.