Load a DLL library from Rhino Plugin

I am stuck in trying to load a DLL library from inside a Rhino plugin written in C#.NET.
First of all, I have to say that if I write a simple console app and call the class exposed by the DLL everything works correctly, since the DLL was already registered by an installer that installed a software a registered many DLLs.
This is a 32-bit DLL. Maybe this is important.

Problems arise when I switch to a Rhino plugin.
I get the error

Class not registered (Exception from HRESULT: 0x80040154 (REGDB_E_CLASSNOTREG))

If I try with the good old regsvr32.exe I get this error

.dll was loaded, but the DllRegisterServer entry point was not found

If I try with regasm /tlb I get

RegAsm: error RA0000 : Unable to locate input assembly ‘myplugin.dll’ or one of its dependencies

I wonder why with a simple console app, simply adding a reference to the DLL, everything is working, while with Rhino it isn’t.

Thank you for any help.

32bit DLLs will not work in Rhino 6 which is a 64bit application

Ouch, ok.

So, switching to Rhino 5 32bit should help?

That would be one option. For 64 bit you would need to either recompile the DLL or create a separate console application that you shell execute from Rhino.