VSIX: AppDomain CreateInstanceAndUnwrapError

I have created AppDomainSetup and applied to console project and it works fine. But when I applied it with VSIX, it doesn't work and I don't know why. Could you someone look into it and help me get out of it. Thanks in advance.

public class Proxy : MarshalByRefObject

{

    public Proxy()
    {

    }
    public Type[] GetTypes(string assemblyName)
    {
        var assembly = Assembly.LoadFile(assemblyName);
        return assembly.GetExportedTypes();
    }

}

The code on VSIX MenuItemCallback

    private void MenuItemCallback(object sender, EventArgs e)
    {
        string message = string.Format(CultureInfo.CurrentCulture, "Inside {0}.MenuItemCallback()", this.GetType().FullName);
        string title = "ProxyCommand";

        var cachePath = Path.Combine(@"D:\Temp", "ShadowCopyCache");
        var pluginPath = Path.Combine(@"D:\Temp", "Plugins");
        if (!Directory.Exists(cachePath))
        {
            Directory.CreateDirectory(cachePath);
        }

        if (!Directory.Exists(pluginPath))
        {
            Directory.CreateDirectory(pluginPath);
        }
        var setup = new AppDomainSetup
        {
            CachePath = cachePath,
            ShadowCopyFiles = "true",
            ShadowCopyDirectories = pluginPath
        };

        domain = AppDomain.CreateDomain("MyDomain", AppDomain.CurrentDomain.Evidence, setup);

        domain = AppDomain.CreateDomain("MyDomain", AppDomain.CurrentDomain.Evidence, setup);
        var proxy = (Proxy)domain.CreateInstanceAndUnwrap(typeof(Proxy).Assembly.FullName, typeof(Proxy).FullName);
        var types = proxy.GetTypes("TestAssembly");           
        AppDomain.Unload(domain);
    }