No SharePoint Server 2007 Service Pack 2 .msp files are installed if you have the Stswwsp1.msp file in the Updates folder

When you try to upgrade Windows SharePoint Services 3.0 Service Pack 2 (SP2) to Microsoft Office SharePoint Server 2007 Service Pack 2 (SP2) by using a slipstream scenario, no SharePoint Server 2007 SP2 .msp files are installed. This issue occurs if you have the Stswwsp1.msp file in the Updates folder.

To resolve this issue, delete the Rtswwsp1.msp file or any other pre-Service Pack 2 .msp files from the Updates folder before you try to upgrade.