Hello All,
While upgrading the GUI to SharePoint 2013 I'm facing an error message saying missing site template. After analysis I reached to a point that sites that were created using FAB 40 template are causing the issue and ultimately failing the UI to be upgraded. Just to clarify the FAB 40 sites that were migrated are working fine on SP 2007, SP 2010 (with SP 2007 GUI) and 2013 (with SP 2007 GUI).