This post is about an error we encountered during the installation of the Microsoft BizTalk Server 2006 R2 Leap Year Date Hotfix (See KB article 2435900 for details). The hotfix requires a certain product version key for Microsoft BizTalk Server 2006 R2, while this product version key is too low when the necessary prerequisites are installed. In this post you can also see the workaround I’ve found to deal with this error.