Does Scratch Link not show up in your system tray? It sounds like Scratch Link is open on your computer and you are trying to re-open it. Opening the program a second time will fail in exactly the same way you are describing. If you see that error, first check the system tray to see if it's open already. Then you can double check the version number by right clicking on it in the tray. It should be version 1.3.66.

If it doesn't look like it's in the system tray you should use the command prompt to quit the process by the id number given in the error. Then relaunch Scratch Link and see if it appears in the system tray.

BrycedTea wrote:

Does Scratch Link not show up in your system tray? It sounds like Scratch Link is open on your computer and you are trying to re-open it. Opening the program a second time will fail in exactly the same way you are describing. If you see that error, first check the system tray to see if it's open already. Then you can double check the version number by right clicking on it in the tray. It should be version 1.3.66.

If it doesn't look like it's in the system tray you should use the command prompt to quit the process by the id number given in the error. Then relaunch Scratch Link and see if it appears in the system tray.

It does show up in my tray, but I don't see Scratch Link open.
.
My SL version: Scratch Link 1.3.66 (f8836d8)
Win32NT

But good news! It works! It's because when it's in the tray, it's running. I didn't understand that until today. Just connect the micro:bit and open the editor, and it should work.
Thank you, @BrycedTea

Edit: I'll close this topic now that it works for me.

Scratch Link does not have a window that opens. There is only the icon in the tray. If you see it in the tray, Scratch Link is open.