Try as you might, you will find that it is impossible to upgrade Windows Vista Service Pack 1 to a previous edition of the operating system, namely Vista RTM. And if upgrading Vista SP1 to the gold version of Vista sounds like a contradiction, just bear with me, it does make sense. The fact of the matter is that with the advent of Vista, Microsoft has introduced the Windows Anytime Upgrade feature. Windows Anytime Upgrade is designed to permit end users to upgrade more basic editions of the latest Windows client to feature-rich SKUs. The Home Basic, Home Premium and Business editions can all be upgraded to Vista Ultimate, with Home Basic also having the option to move to Home Premium.

"Consider the following scenario," Microsoft said. "You have Windows Vista Home Basic installed on the computer. Or, you have a similar version of Windows Vista installed on the computer. Then, you install Windows Vista Service Pack 1 (SP1) on the computer. Then, you try to upgrade to a version of Windows Vista that has additional features. For example, you try to upgrade to Windows Vista Ultimate. To perform the upgrade, you use Windows Vista media that does not contain the updates that are included in Windows Vista Service Pack 1."

Using Windows Anytime Upgrade to upgrade an edition of Vista SP1 to Vista RTM will not result in a successful operation. "In this scenario, you receive the following error message: 'The upgrade cannot be started'," Microsoft added. "Then, you receive the following error message: 'To upgrade, cancel the installation and then choose to upgrade to a version of windows that is more recent than the version you are currently running'."

The Redmond company has informed that the issue is related to the incongruence between the contents of the Vista RTM media and those of Vista SP1. Namely it is the difference in updates contained in Vista SP1 in comparison to Vista RTM that makes the upgrade impossible. A successful move between Vista Service Pack 1 editions is possible through Windows Anytime Upgrade, provided that the media also contains the SP1 bits.

"To resolve this issue, upgrade the computer by using media that contains the updates that are included in Windows Vista Service Pack 1," the company stated, pointing to the computer's manufacturer as the source of the media. "If you do not have access to Windows Vista media that contains the updates that are included in Windows Vista Service Pack 1, you must remove the service pack from the computer and then upgrade the computer."

Windows Vista Service Pack 1 Five Language Standalone for both 32-bit and 64-bit versions of the operating system is available for download HERE.