I've made a mistake: in our situation two users try to launch the program as an administrator. So eventually the program couldn't run twice from one user (administrator).

However, you've given an exhaustive answer. We will try to do what you suggested. Thank you.

Now I'll try to explain our ...

We've made a runnable jar and given copies of it to different users on one computer (working on two desktops). But only one of them can run the program at a time. When the second tries, the new process starts and dies immediately. But we really need two and more users working with SH3D at the same ...