The Fabulous 40 (a.k.a. Fab40 or Application Templates) are a set of 40 application templates for Windows SharePoint Services 3.0. These were installed on a lot of SharePoint 2007 environments.

When upgrading to SharePoint 2010 these templates become a challenge. The sites based on the Site Admin Templates (.STP) will be upgraded. After the upgrade these will likely work, but you can’t create any new sites based the STP templates, because SharePoint 2010 does not support STP files for site templates.

Sites which are based on the Server Admin Templates (.WSP) are more challenging because some Fab40 templates cannot be used for creating new sites in SharePoint 2010. To perform an upgrade you need to install the templates which are currently in use in the SharePoint 2007 environment.

To keep the new SharePoint 2010 environment as clean as possible you want to disable the creation of new sites…