Where to find information on DWG TrueView development

Where can I found out what I can and can not do in the DWG TrueView application. I've created a test DLL using VB.Net and loaded it into the viewer but there is this message that keeps appearing when the DLL is loaded.

Error Message in Viewer command line.
Cannot load assembly. Error details:
System.Security.SecurityException: Security error.
at
Autodesk.AutoCAD.ApplicationServices.ExtensionLoader.ProcessAssembly(Assembly
assembly)
The Zone of the assembly that failed was:
MyComputer

The DLL displays a simple dialog box and contains a button to list the layouts in the active drawing. The form does load and work correctly. I don't fully understand the error, something to do with the new security settings in .Net 2.0 I assume.

I assumed that TrueView was locked down like most other OEM packages and that you could not run 3rd party code from within (unless of course you are the 3rd party developer and the OEM is licensed to you...)