How to maintain Lotus Notes Version ? C#

I made one product which is retrieving attachment from mails and saving it on particular folder.

But problem i am facing is it is not working in 8.0 version. I did development on Lotus Notes 8.5 version.

I used tried:

object obj =
  Activator.CreateInstance(Type.GetTypeFromProgID("Notes.NotesSession"));

But still facing same problem.

If you are looking to check the Notes version number, you can do this through the NotesBuildVersion property of the Session class. This is a long int, with each Notes client version having a distinct value.

8.0 will have build number of 301 (or higher) 8.5 will have build number of 323 or higher

See this technote for a (nearly) complete list; also this blog post