Type mismatch error MyFunc(arg1), MyFunc is out-of-proc COM and arg1 is IUnknown**

[GuyHarel]

Hello
I am trying to interface with a legacy MFC out-of-proc COM server. Some by ref arguments work fine (like long*) the other (IUnknown**) give me a DISP_E_TYPEMISM ATCH, no matter what I try. Example:

COM server:

long CNAVDocViewer::getMainWindowHandle(long* _plhWnd)

VB.NET:

Dim o As Object = CreateObject("NAVDocViewer.NAVDocViewer")
Dim h As Integer = Integer.MinValue
o.getMainWindowHandle(h)

Works...getting the right value, however:

COM server:

long CNAVDocViewer::closeAllDocument(IUnknown**	_ppitfEreur)

VB.NET
(I've tried all the following types, none works)

        ' DISP_E_TYPEMISMATCH
        Dim err As Object = Nothing ' No
        Dim errDQS As aDQSErrorServr.DQSEror = New aDQSErrorServr.DQSEror ' No
        Dim errDQSI As aDQSErrorServr.IDQSEror = Nothing ' No
        Dim i As Int32 = 0 ' No
        Dim s As String = "" ' No... :)
        Dim p As IntPtr = Nothing ' No
        Dim p1 As IntPtr = New IntPtr(0) ' No
        Dim p2 As IntPtr = Marshal.GetIUnknownForObject(errDQS)  ' No

        o.closeAllDocument(errDQSI)

The value returned by the COM server is NULL if no error happened in the function, otherwise a DQSERROR COM object.
I spend two days reading articles on this and IntPtr should do the job, followed by Marshal.QueryIn terafce() but it does now work.

Any help would be appreciated. Tx.

[GuyHarel]

Solved by the MSDN guys:

http://social.msdn.microsoft.com/Forums/en-US/clr/thread/75434221-a082-4d6c-ab2a-a38433da5a19/