My current DNN version is 4.3.5. I was able to successfully upgrade to 4.4. My next step was to upgrade it to 4.6. I copied the installation package, copied all files that were modied in my earlier DNN version, updated the web.config file and then ran the upgrade. All the reports on the initial upgrade page was successful. It said "Click here to access your portal" and when i click it, it gives me the following error -

___________________________________________________________________________________________________________[ArgumentNullException: Value cannot be null.
Parameter name: type]
   System.Activator.CreateInstance(Type type, Boolean nonPublic) +7467190
   DotNetNuke.Framework.Reflection.CreateObject(String ObjectProviderType, String ObjectProviderName, String ObjectNamespace, String ObjectAssemblyName, Boolean UseCache) +584
   DotNetNuke.Framework.Reflection.CreateObject(String ObjectProviderType, Boolean UseCache) +26
   DotNetNuke.Security.Membership.MembershipProvider.CreateProvider() +31
   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.GetUserCountByPortal(Int32 portalId) +0
   DotNetNuke.Entities.Portals.PortalInfo.get_Users() +20
   DotNetNuke.Entities.Portals.PortalSettings.GetPortalSettings(Int32 TabId, PortalAliasInfo objPortalAliasInfo) +1693
   DotNetNuke.Entities.Portals.PortalSettings..ctor(Int32 tabId, PortalAliasInfo objPortalAliasInfo) +76
   DotNetNuke.HttpModules.UrlRewriteModule.OnBeginRequest(Object s, EventArgs e) +2240
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +68
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +75
___________________________________________________________________________________________________________

i made sure that the changes to web.config are replicated correctly (including the machine key). All the dll's seems to be copied fine. The network service account has the right permission on the folders. What does this error mean and how to fix this? I had almost the same web.config file when i upgraded to 4.4 and everything worked so smoothly...The upgrade to 4.6 seems so complex. Anyways, thanks in advance guys.

I have configured my own custom membership provider. And I am using that dll within the bin folder. The very same custom memership provider worked fine when i upgraded to 4.4. Is it possible that the custom membership provider has a reference to the old dotnetnuke dll and needs to be updated to the new dotnetnuke dll? But as far as copying the correct membership dll into bin folder and updating the web.config, I am very certain that I updated them correctly. Thanks.