🚀 go-pugleaf

That's correct, edit and debug. Selecting edit should launch "ExtendScript Toolkit.exe" and load the script currently selected in the scripts panel. A shortcut for this is holding down the Alt key and double clicking a the script to edit, in the sctipts panel.

Since you say "The toolkit is installed", I assume that you've started it and that it works? Until you find out what's wrong you will have to start the "Adobe ExtendScript Toolkit CS4" manually from disk or from the start-menu. You could also Ctrl+doubleclick a script file in the scripts panel to show it in Windows Explorer, and then select to Open with the extend script toolkit.
A few extra steps to open it up, but the same result if it works. But until someone else comes with a better idea...

I had a similar problem once with another program... I had had my computer attached to a projector - meaning two screens. When back on my normal screen only, one dialogue box which had been closed on the other screen still opened up at those coordinates, and "at the other screen", i.e. outside what I could see on the single screen.