static extern int VarBstrFromDisp(IntPtr Disp, int lcid, int dwFlags, [MarshalAs(UnmanagedType.BStr)] out string pbstrOut);

Declare Function VarBstrFromDisp Lib "oleaut32.dll" (Byval Disp as IntPtr, Byval lcid As Integer, Byref pbstrOut as String) As Integer

   int hr = VarBstrFromDisp(Marshal.GetIDispatchForObjectInContext(pComObject), Thread.CurrentThread.CurrentCulture.LCID, 0, out pbstrOut);

See also VarBstrFromDisp