No, problem, glad to help. I have been using Construct 2 for a few weeks, so still not intimately familiar with all it's inner workings, but my development background tends to come in handy for figuring out how to resolve issues with game play mechanics in C2.
I tend to try to find the simplest solution in order to avoid having the underlying code check for too many things at once as any unnecessary calls could potentially slow the game down.
I haven't had time to look at your updated capx, but if you don't have an answer by the time I get home tonight (pacific time U.S.) I will take a look. Though that won't be for a good 12 hours.
The problem off the top of my head is that you need to detect which echo has been clicked then have the key display. You may want to do something like have the key check if the nearest echo is visible. And if it is, then go ahead and set the key to invisible and start the fade. You could also do something like create a variable, and when clicking on the echoes have them set that variables value, then you can have your key check the value of the variable, if it is set to the value you want (maybe true/false type value Boolean) then if it is true have the key set it back to false, turn visible, then start its fade out. This will keep it from having the same issue you had before where the fade would keep repeating.
So something like this:
1. Have the Echo check if it is overlapping the key when you click it.
2. If the echo is overlapping the Key set the variable (overlapKey) to true (make sure the variable is set to false when it is created).
3. Have an condition that checks if "overlapKey" is true, Set it to false, set the key to visible, and start fade out. (Setting the variable back to false is key here as it makes it so the key does not keep repeating it's fadeout).
At that point the key is ready for the next echo event to happen. You have also eliminated having to tell it which echo is the right one as the echo will take care of that for you in it's check to see if it is overlapping the key. You just need to have each echo make that check when clicked on and set the variable accordingly.
Hope this helps!