John, i'm sorry, but i'm confused now 
This is the way i set up my projects:
* solution file in /solutions folder
* reference the dnn project (not the dnn.dll)
Until asp.net 2.0 came around that was a perfectly good way to set up projects.. (at least i thought so)
>The error is because the ML SkinObject was compiled into an older version of DotNetNuke.
> If you compile it into the current version you are trying to use, it should work.
the module that contains the skinobject was compiled into dnn 3.2.2, so thats the latest version. Further more, it was not compiled into dotnetnuke.dll, but into its own dll. This module was review by Joe Brinkman for the dnn marketplace...
Cheers,
Erik