My current app runs on DNN 4.3.5. I am trying to upgrade it to 4.9.4. I downloaded the install package and followed the instructions and it said "Upgrade was successful. Click here to access the portal". When I try to access the portal, i get the following error -  "Value cannot be null. Parameter name : type. The type initializer for 'DotNetNuke.Security.Membership.MembershipProvider' threw an exception. The type initializer for 'DotNetNuke.Entities.Users.UserController' threw an exception". I came across this thread where they mentioned that i have to remove some old dll's. I am just using the install version and hence i do not have old dll's. However i have a custome membership provider dll and profile provider dll that still has reference to dnn 4.3.5. Would that be causing this error message? Apart from those custom membership and profile provider dll, i do not have any other old dlls. Any thoughts/ideas?

You said "When upgrading from DNN 4.3.5, I suggest to perform it in multiple steps, via DNN 4.4.1 and 4.6.2"

How do I get hold of DNN version 4.6.2 as you have suggested. Do I download the install or upgrade versions  and from what website?

Thanks in advance

Raj

I'm running into a similar "Null" error when I try to open the website after upgrading a v4.6.2 site to v4.9.4

The error is "Value cannot be null. Parameter name: replacement"
A screen cap of the entire error is shown below.
The rest of my upgrade went OK with the functionality of the portal preserved.
My upgrade path was 3.2.2 -> 4.3.7 -> 4.4.1 -> 4.6.2 -> 4.9.4
I found that even though I was at 4.6.2 I still had to edit the SQL connection string in the web.config file prior to install.
I haven't been able to connect to check the status of my user accounts (100's).

I can't agree with others here or stress enough how important good backups are!!!