Activator.CreateInstanceFrom and referenced assemblies-Collection of common programming errors

After reading “Discover Techniques for Safely Hosting Untrusted Add-Ins with the .NET Framework 2.0” by Shawn Farkas in November 2005 MSDN issue (

) I wrote a simple program to test it. The directory structure is (directories are in bold):

HostApp  HostApp.exe  Interfaces.dll  AddinMgr.dll

  Addins

    Test
      TestAddin.dll

Interfaces.dll assembly has two interfaces: IHost and IAddin. AddinMgr.dll contains one class AddinManager which implements IHost. TestAddin.dll contains one class Test which implements IAddin.

I create a new application domain with ApplicationBase pointing to Addins\Test and then use Activator.CreateInstanceFrom to create an instance of AddinManager class in a new domain. Then AddinManager calls Activator.CreateInstance to create an instance of Test class. This is where the problem is: Activator.CreateInstance throws FileNotFoundException (could not load file or assembly ‘Interfaces’). But AppDomain.GetAssemblies() shows that Interfaces.dll was loaded in the new domain. If I copy Interfaces.dll in the Addins\Test directory then everything works.

So, my question is: how does CreateInstanceFrom(AppDomain appDomain, string assembly, string type) really works? It looks like assemblies loaded with CreateInstanceFrom are being treated differently by the runtime.

Alex