I updated my blog post:
Wednesday, August 26, 2009 10:33 AM
on 01/Sep/2009 and we know now more about that issue.
You may detached your content databases before upgrade SharePoint to WSS August CU. After the successfully installation of WSS August CU you are trying to re-attach the content databases. That fails.
Current idea for a solution:
MOSS 2007 and WSS V3 are affected applications with WSS August CU. This procedure is currently the best known way.
More information should be shortly available on my colleagues blog http://blogs.msdn.com/gyorgyh/
926961 Error message when you use SharePoint 3.0 Central Administration to try to re-add a content database in Windows SharePoint Services 3.0 http://support.microsoft.com/default.aspx?scid=kb;EN-US;926961