When installing Visual Studio 2008 Sp1 Beta1, you may encounter an error that you must first remove KB944899 before setup can continue. This message can be displayed if you have installed any KB for Visual Studio 2008, not just KB944899.
You can download and run this executable which will remove KB944899 if needed and remove the registry keys that are causing the problem.
Alternatively, you can work around this problem manually as described by Heath here: http://blogs.msdn.com/heaths/archive/2008/05/16/kb944899-should-be-removed-before-installing-visual-studio-2008-sp1.aspx
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