Lotus Domino on 64 bit system: Could not create automation object, error 208 - com

Question

I have created a C# .NET DLL with Release/AnyCPU as per http://www-01.ibm.com/support/docview.wss?uid=swg21230705 and successfully registered it for COM Interop.
When I open my 32bit Excel on a 32bit Windows 10, and use the code
Private Sub CommandButton1_Click()
Dim obj As Variant
Set obj = CreateObject("MyTest")
MsgBox obj.AppendStr("This is")
End Sub
it returns the expected values. When I open 32bit Excel on a 64 bit Windows 8.1, and use the same code, it also returns the expected values. The same goes for a similarly crafted VB6 executable deployed on both systems.
But when I try the same from Notes 32 bit using the code
Sub Click(Source As Button)
Dim obj As Variant
set obj = CreateObject("MyTest")
MsgBox obj.AppendStr("This is")
End Sub
it returns the expected values on a 32 bit Windows 10
it throws the error "Could not create automation object" on a 64 bit Windows 8.1
Furthermore, and this is the most interesting part for me, it throws "Could not create automation object" when run as a LotusScript http agent on the Domino 64 bit server on a 64 bit Windows Server system.
Do you have any ideas how I could get the DLL function call to work with both 32 as well as 64 bit Lotus Domino Server?
Or are there any other ways to call a single function in my C# DLL from Notes, which takes a single string as parameter and returns a byte array? (e.g. through a Java agent, through a Domino shell object, or both?)

Answer 1

I just found the solution, and it wasn't a Domino problem at all. The linked tutorial is for pre-64bit systems and says:
To make the objects in this DLL accessible via the COM interface, enter the following command:
regasm MyTest.dll
Since the introduction of AMD64, you have to read this step as follows:
To make the objects in this DLL accessible via the COM interface for both 32 bit and 64 bit applications, enter BOTH the following commands:
%Windir%\Microsoft.NET\Framework\<version>\regasm MyTest.dll
%Windir%\Microsoft.NET\Framework64\<version>\regasm MyTest.dll
I only did the first, which made it work for 32bit, but not for 64bit.

Answer 2

To answer the question in a technical aspect, you can call yout 32 bits DLL by copying it to Windows\SysWow64.see Can a 64 bit EXE link against 32-bit DLLs? for more details.
To answer your need we just need to transform a string to byte array.
You can do this in java and use ls2j to call it.
I also think to use the lib of native consumer to dothis.
Look also at https://www.experts-exchange.com/questions/23120423/Using-NotesStream-to-convert-a-string-to-a-byte-array.html it give you a lotuscript solution.