I have recently tried to upgrade from 4.0.1 to 4.3.7.  The upgrade process ran without reporting any erros but when I try to access my portal I get this error message:

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

[NullReferenceException: Object reference not set to an instance of an object.]
   DotNetNuke.Framework.Reflection.CreateObject(String ObjectProviderType, String ObjectProviderName, String ObjectNamespace, String ObjectAssemblyName, Boolean UseCache) +465
   DotNetNuke.Security.Membership.MembershipProvider.CreateProvider() +38
   DotNetNuke.Security.Membership.MembershipProvider..cctor() +13

[TypeInitializationException: The type initializer for 'DotNetNuke.Security.Membership.MembershipProvider' threw an exception.]
   DotNetNuke.Security.Membership.MembershipProvider.Instance() +0
   DotNetNuke.Entities.Users.UserController..cctor() +5

[TypeInitializationException: The type initializer for 'DotNetNuke.Entities.Users.UserController' threw an exception.]
   DotNetNuke.Entities.Users.UserController.GetCurrentUserInfo() +0
   DotNetNuke.Services.Exceptions.BasePortalException.InitilizePrivateVariables() +245

Any help is much appreciated

Déclic Vidéo FX, I believe that is the correct process if you are using the UPGRADE package, not the install package. I read somewhere that using the INSTALL package messes up some stuff if you alread have a version installed.

On a separate note, I have upgraded from 4.0.2-->4.3.7-->4.4.0. Each time I had to go into the database tables and change the ApplicationId for each of my members because it didn't update that. Is this something specific to a particular module I have installed (I have Active Forums) or is it something that DNN does (adding new application ID's) when upgrading? The table shows four diffent applications installed, but I have only 1 portal. The id's are "/", "0", "-1", and "dotnetnuke", the last one is the latest for 4.4.0. I should also note that I could not log in until I change the ApplicationId in the database, but I could see the site as a non-registered user.

Stubs, how did you upgrade from 4.0.2 to 4.3.7/4.4.0 while keeping your Active Forums data, is it easy or you had to play around with the database? Would really appreciate any hints cuz I'm in a bit of a muddle!