You may face this error while Adding / Removing features from Visual Studio 2008 if SP1 is already installed. One of the workaround is to uninstall SP1 before this operation and install it again after performing this operation. However, this can be tedious.

There is a hotfix which addresses the Upgrade issue for the product setup launched from Windows Add/Remove Programs dialog. Visual Studio 2008 setup launched from installation media remains unaffected.

The hotfix can be downloaded from here:

https://connect.microsoft.com/VisualStudio/Downloads/DownloadDetails.aspx?DownloadID=27638

There is another issue where in the maintenance mode of Visual Studio might ask for a file called SQLSysClrTypes.msi.This file is present in Visual Studio SP1 package. The workaround for this solution is given here:

http://blogs.msdn.com/b/heaths/archive/2009/02/02/feature-changes-in-visual-studio-2008-sp1-may-prompt-for-sqlsysclrtypes-msi.aspx?wa=wsignin1.0