Success! I was having the same sequence of errors. I strongly suspect that the root of the issue was missing the Default.page.template file in one or more of the Portals/[PortalID]/Templates directories. However, here are some other things I did based on this and other forum posts:

Low probability of impact items, but I saw various references, so I figured I'd do it.
1. I installed the latest XML Module (I didn't have the XML module installed at all)
2. I updated all my modules to the latest version my install (4.9) would support

Higher likelihood these changes mattered
1. Make sure each Portal/[Portal ID]/Templates folder has the Default.page.template file
2. After downloading the upgrade package, right-click on the zip file, select properties and then click 'Unblock' (I did this directly on my server)
         Unzip the upgrade package to its own folder
         Copy the package files over the top of your DNN install (replacing files)
3. Ensure permissions are correct for the ApplicationPool service account on your wwwRoot folder.

IIS 6: Network Service Account
IIS 7/7.5 Has a new permission model (This is default on 7.5)! Your site may be using this
The only way to set the permission is through the command line interface:
>icacls [PathToDNNInstallRoot] /grant "IIS AppPool\[NameOfAppPool]":(OI)(CI)F
This grants Full access to the isolated Application Pool account at the root of your DNN and sets inheritance on all folders and files. You can verify this on the security tab of the files/folders, you just cant set it there.
example:
>icacls C:\WebSites\DotNetNuke-1\DNN_Prod\wwwRoot /grant "IIS AppPool\DotNetNuke-1_Prod":(OI)(CI)F

It's so nice to see all of the green Success! lines.

Best of luck to others experiencing these issues, they can be overcome. I hope this post helps. Don't give up, because even though it may look like your site is working, some of the new menu items in admin/host won't be there (noteably Taxonomy-- this should be an admin menu item.