Dur! I should have thought about deleting the prefs file.
Ok. I did it. But it didn't mitigate the problem. When I click on the app, it launches for about one second, appears in the dock and immediately disappears...😡
When you try and open it, does it just not open the main window? I've had this before. I thought it was broken, when actually it was open, and all I had to do was click Window->Activity Monitor (or something like that!)
I think they probably mean repairing permissions in the usual sense, via the Disk Utility program. There is an option there to verify and/or repair permissions for the whole system. Give it a try.