>I have existing sites running DotNetNuke 3.X and would like to upgrade them to the DotNetNuke 4.x code so that they are running under .NET version 2.
>
>Has anyone done this successfully? I've followed steps from the DotNetNuke website, but none work. I end up with either SQL Server errors or "module can't load" errors.

I've asked the same question. It's not easy enough. Incremental upgrades may be best.