SPS2003 Upgrade Error When Upgrading to MOSS 2007: Not detaching landing page

When trying to do the upgrade from MOSS 2007 from SPS 2003 you may receive an error in the event log that resembles the following:

[PortalSiteUpgradeAreaAndListingData] [12.0.1.0] [INFO] [1/10/2007 12:37:59 PM]: Upgrading pages for area at "https://servername/C5/SiteA".
[PortalSiteUpgradeAreaAndListingData] [12.0.1.0] [DEBUG] [1/10/2007 12:37:59 PM]: ENTER -- PortalSiteUpgradeAreaAndListingData::UpgradeOOBPages
[PortalSiteUpgradeAreaAndListingData] [12.0.1.0] [INFO] [1/10/2007 12:37:59 PM]: Not detaching landing page from page layout because it is not customized.
[PortalSiteUpgradeAreaAndListingData] [12.0.1.0] [INFO] [1/10/2007 12:37:59 PM]: Moving v2 database landing page content and webparts to v3 landing page...
[PortalSiteUpgradeAreaAndListingData] [12.0.1.0] [INFO] [1/10/2007 12:37:59 PM]: Error moving landing page "https://servername/C5/SiteA/default.aspx": Folder "Pages" does not exist..  Upgrade cannot continue.
[PortalSiteUpgradeAreaAndListingData] [12.0.1.0] [INFO] [1/10/2007 12:37:59 PM]: Upgrade encountered an unexpected error.  Halting upgrade...
Microsoft.SharePoint.SPException: Folder "Pages" does not exist. ---> System.Runtime.InteropServices.COMException (0x8107021A): Folder "Pages" does not exist.
   at Microsoft.SharePoint.Library.SPRequestInternalClass.MoveUrl(String bstrUrl, String bstrWebRelOldUrl, String bstrWebRelNewUrl, Int32 grf)
   at Microsoft.SharePoint.Library.SPRequest.MoveUrl(String bstrUrl, String bstrWebRelOldUrl, String bstrWebRelNewUrl, Int32 grf)
   --- End of inner exception stack trace ---
   at Microsoft.SharePoint.Library.SPRequest.MoveUrl(String bstrUrl, String bstrWebRelOldUrl, String bstrWebRelNewUrl, Int32 grf)
   at Microsoft.SharePoint.SPFile.MoveCopyInternal(String strNewUrl, Int32 grf)
   at Microsoft.SharePoint.SPFile.MoveTo(String newUrl, SPMoveOperations flags)
   at Microsoft.SharePoint.Portal.Upgrade.PortalSiteUpgradeAreaAndListingData.UpgradeOOBPages(AreaData SPSArea, PublishingWeb CMSArea)
   at Microsoft.SharePoint.Portal.Upgrade.PortalSiteUpgradeAreaAndListingData.UpgradePages(AreaData SPSArea, PublishingWeb CMSArea)
   at Microsoft.SharePoint.Portal.Upgrade.PortalSiteUpgradeAreaAndListingData.RunUpgradeLoop1(SPSite site, AreaData SPSArea, Int32 parentPermId)
   at Microsoft.SharePoint.Portal.Upgrade.PortalSiteUpgradeAreaAndListingData.RunUpgradeLoop1(SPSite site, AreaData SPSArea, Int32 parentPermId)
   at Microsoft.SharePoint.Portal.Upgrade.PortalSiteUpgradeAreaAndListingData.RunUpgradeLoop1(SPSite site, AreaData SPSArea, Int32 parentPermId)
   at Microsoft.SharePoint.Portal.Upgrade.PortalSiteUpgradeAreaAndListingData.Upgrade()

This may be due to the fact that the site being upgraded uses a specific site template that doesn't have a mapping to a MOSS template.  Thus, the upgrade for this site fails.

For those sites with a custom site template, there has to be some development work done in order to migrate those.  The following URL leads to an upgrade article for sites with custom site templates that will require you to use some steps in the WSS 3.0 upgrade solution accelerator to move them.  Basically, you have to prep an upgrade definition prior to the upgrade.  This will have to be done for all custom site templates. 

https://www.microsoft.com/technet/solutionaccelerators/collaboration/utwssst3.mspx

Basically, once you build the upgrade definition file you place it in the \upgrade directory where the upgrade process looks at it and processes it during the upgrade.