Microsoft has released a Knowledge Base article detailing a Windows XP to Windows Vista upgrade issue. According to the resource made available by the Microsoft support team because of language pack issues between the two operating systems, users will not be able to upgrade certain versions of Windows XP to Windows Vista.

"Windows Vista is available in 36 languages. This includes 11 languages that are available in Windows XP only if you use a Windows XP Language Interface Pack. However, you cannot upgrade a Windows XP-based computer that is running one of these packs to a version of Windows Vista that uses one of the new languages. If you try to do this, the Upgrade option is not available. Instead, you must perform a custom installation of Windows Vista or a clean installation of Windows Vista," reads a fragment of KB 932856.

The following list of XP language versions are affected by this issue: Bulgarian, Croatian, Estonian, Latvian, Lithuanian, Romanian, Serbian-Latin, Slovak, Slovenian, Thai and Ukrainian. Microsoft's explanation for this problem is the fact that the operating system language in Windows XP fails to match the language of the Windows vista copy that is installed.

The Traditional Chinese, Czech, Danish, Finnish, Norwegian (Bokmål), Polish, Portuguese (Portugal), Russian, Spanish, Swedish and Turkish editions of Windows Media Center Edition 2005 also generate issues when users attempt to upgrade to Windows Vista.

"Although you may be unable to upgrade the computer to Windows Vista, you can perform a custom installation of Windows Vista. A custom installation helps preserve the data files from an earlier installation of Windows XP," is the only workaround delivered by Microsoft.