title: C# Com E_NOINTERFACE Queryinterface
body: <p>I am sorry but I have to ask again. I am searching since many weeks and month for a solution now. 
  The Problem is that have implemented a COM-Interface the throws only by calling a few methods an InvalidCast Exception E_NOINTERFACE and it tells me that I have to implement IUnknown.
  So how can I do that?</p>
  
  <p>I tried nearly everything...
  Currently I have something like this</p>
  
  <pre><code>[ComImport,
   Guid("279AFA85-4981-11CE-A521-0020AF0BE560"),
   InterfaceType(ComInterfaceType.InterfaceIsIUnknown),
   System.Security.SuppressUnmanagedCodeSecurity]
  
  public interface IDirectSoundBuffer : IUnknown
  {
  </code></pre>
  
  <p>...</p>
  
  <pre><code>[ComImport]
  [Guid("00000000-0000-0000-C000-000000000046")]
  [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
  public interface IUnknown
  {
      void QueryInterface([In] ref Guid giid, [Out, MarshalAs(UnmanagedType.IUnknown, IidParameterIndex = 0)] out object ppvObject);
      [PreserveSig]
      uint AddRef();
      [PreserveSig]
      uint Release();
  }
  </code></pre>
  
  <p>I really don t know what I could try more. I had on many different forums a topic discussing this but noboboy knows anything :(( pls help me.</p>