Rhino3 install .DLL Plugin

There is a Rhino3 plugin wich is provided as a folder including following dlls:

-de [folder: contains MyPlugin.Ressorces]

Rhino3s plugin-manager accepts only .rhp plugins to install. Rhino3-Net SDK is installed. I get allways attribute-error also for sample plugins from SDK when i try to install .dll with DotNetManager-Plugin?

This is just for testing and to get a basic feeling about it.
The actual task is is to rebuild this plugin for use with Rhino5 (Plugins C#-Source-Code is present)

Man, it has been quite a while since Rhino3. I can’t remember how the how our .NET SDK was structured back than; I know it was only an early prototype at the time.

Plug-ins are just DLLs renamed as RHP. You might want to try renaming MyPlugin.dll to MyPlugin.rhp to see if that works. That is only a guess though.