I have been having this same problem for over a week.  There is an existing 3.3.7 site I wanted to upgrade to 4.4, but it didn't seem to work.  Since 4.4 isn't really 100% yet I decided I would attempt to upgrade to 4.3 instead.  When upgrading to 4.3 I had the same problem as going to 4.4.

When I start the process, I install a fresh install of 4.3, create a new database for it, and let it install its self.  After 4.3 is installed, I make sure my modules are all installed.  Once the modules are installed I make a new batabase and import the data from my current production site.  I then point the web.config for the new site to this copy of my production database (also copy over keys), and copy the portals from my production database to the 4.3 portals folder.  Once this is done and all the permissions are correct, I goto the 4.3 site.  It starts upgrading for a slit second, but throws an error to the log.  In my last post I posted a snippet from my log, but I can do so again.  Basically the first error listed is System.Data.SqlClient.SqlException: Invalid object name 'dbo.aspnet_Membership_UpdateUser'.

Please, what am I doing wrong.  The primary guide I was following was this one at datasprings (http://www.datasprings.com/default.aspx?tabid=738).  Any help would be great.

Ok, I think I got farther this time.  I got it to run the upgrade successfully by restoring a backup of my production database, copying my portals into a working 4.3 site, changing the web.config to point to the restored database and changing the keys to match the old sites web.config.  It ran through and didn't have any errors, but the portal it shows is not the one I am trying to get it to upgrade to, and it doesn't seem to have anything it should.  Basically it looks like a blank DNN site without any modules and using the default skin.