Cannot load assemblies in sub-directories

[pzero24]

Ok so I am making plugins for my application and I have the plugins located in a subdirectory:

/AppDir
/AppDir/Plugins

All my plugins reference a Plugins interface file, which is also located in the Plugins subdirectory. I used AppDomainSetup.PrivateBinPath property to have it probe the subdirectory, but when I try to load it into my AppDomain it throws an error:

Could not load file or assembly 'EmptyPlugin, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.

Which makes me think it can't find the file but when I comment out the PrivateBinPath property it throws me this error instead:

Could not load file or assembly 'EmptyPlugin' or one of its dependencies. The system cannot find the file specified.

So that tells me that it finds the file. When I view the detail of the first error it shows me this:

Source: mscorlib

So the only thing I can think is it can't load mscorlib. But mscorlib is in the GAC so I don't know how it couldn't load. Anyway, heres the code thats throwing the error:

public Plugin(IServer host, string domainName, string filePath)
        {
            AppDomainSetup setup = AppDomain.CurrentDomain.SetupInformation;
            setup.PrivateBinPath = "Plugins";
            pluginDomain = AppDomain.CreateDomain(domainName, null, setup);
            Assembly plugin = pluginDomain.Load(domainName); //Throws the error

If someone could help me that would be greatly appreciated.

[pzero24]

I forgot to say that it is coded in C#