COM interface / class returns "object has no properties or methods" error

Question

I am trying to develop a calculation engine and expose the implemented classes as COM objects following this Article. The exposed DLL (Com Object) is going to be consumed by a third-party application. Some older DLLs implemented by VB6 are now using and working properly.

While the final DLL is registered via RegAsm command in the Command Prompt, the COM object becomes visible in the target application but I receive the error messages of

"Failed to create object", "Object has no properties or methods".

What I have tried so far, in addition to the code below, is listed below :

• ComVisible is set to true in AssemblyIfo.cs
• Checked "Register for COM interop" in Build Options
• Set [ComVisible(true)] attribute on classe/interface and/or method
• Set [DispId(0)] attribute on classe/interface and/or method with different values !!
• Set [ProgId] attribute on classe/interface and/or method
• All methods and classes are defined as public members
• Tried all the above actions to the class with/without interface
• Tried all the above actions to the class with/without event interface

I have created a sample code as an example here, any further help would be appreciated :)

using System;
using System.Runtime.InteropServices;

namespace project_name
{
    [Guid("EAA4976A-45C3-4BC5-BC0B-E474F4C3C83F")]
    [ComVisible(true)]
    public interface ComClass1Interface
    {
        [DispId(0)]
        [ComVisible(true)]
        double calc();
    }

    [Guid("7BD20046-DF8C-44A6-8F6B-687FAA26FA71"),
        InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
    public interface ComClass1Events
    {
    }

    [Guid("0D53A3E8-E51A-49C7-944E-E72A2064F938"),
        ClassInterface(ClassInterfaceType.None),
        ComSourceInterfaces(typeof(ComClass1Events))]
    public class ComClass1 : ComClass1Interface
    {
        public double calc()
        {
            return 13;
        }
    }
}

The DLL is registered using RegAsm command to be listed on COM Objects.

The Com Object becomes visible to the target application.

When trying to select the implemented method I face these errors :-/:

I am using Visual Studio 2019, C#, .NET Framework 4.0 and the target application is running on Windows Server 2008 R2 and .NET Frameworks 3.5, 4.6 are installed.

Answer 1

The issue solved by These actions:

1. The assembly should be signed with a strong name (I used Visual Studio Signing tool)
2. The COM Object should be registered with regasm path/dll-name.dll /codebase /tlb /nologo