COM Interop Conumdrum

[John Puopolo]

All:

I have developed an ActiveX control using MFC. The control has a simple
method defined in the ODL:

[id(101)] void Apple([in] BSTR x, [in] BSTR y, [out, retval] long* ok);

The implementation of Apple sets *ok = 0.

In my C# (Windows Forms) project, I create a reference to the control
and view the wrapper signature:

System.Int32 Apple ( System.String x , System.String y )

This looks correct. Now, I call the function from one of my C# methods:

private void button1_Click(object sender, System.EventArgs e) {
int retval = 0;
retval = ax1.Apple("hello", "world");
}

CLR reports the following error:
An unhandled exception of type
'System.Runtime.InteropServices.COMException' occurred in mscorlib.dll
Additional information: Parameter not optional.

Any ideas? Many thanks...

John