Hi
Well I have been doing some digging, and I now think that the problem is actually related to permission problems when connecting to the database. My reasons are below:
I downloaded the original source again from DNN and built the project from scratch with VS 2005. I configured the database connection using two methods and one worked correctly and one didn't.
The first way that worked has the "identity impersonate=true" set with "Trusted_Connection=true;" on the connection string (both in web.config). IIS anonymous access for the virtual directory then contains a domain account and password (i.e. Unceck allow IIS to manage account password). This worked correctly, and connected to the separate database server. This wasn't what I required though, as I want to identify my end user and automatically log them in (via the Active Directory mechanism). For this to work, I need Integrated Authentication, and Anonymous turned off. So I tried the second way.
The second way has the "identity impersonate=true; userName=xxxxxxxxxx; password=xxxxxxxxxx" set. IIS will then use integrated authentication, and anonymous is turned off. This immediately brings up the assembly error (access denied).
I tried restarting IIS to ensure that this wasn't something to do with cached credentials (etc.), but sadly it wasn't.
All of this worked fine on 4.4.0, so any help and advise on this would be very useful.
Many Thanks
Glen