Should have mentioned (wish I'd remembered to take a screenshot) after a few attempts, and before it actually opens, a sequence of little windows come up with 'K37 not found [OK]', after a few clicks on OK on (maybe five) windows it opens.
It's possible that it's my setup. Unfortunately, due to win7 being orphaned, in quick succession I've installed win10 and FSX:SE.
Managed a screenshot of the 'little windows'.
This one was just a two clicker before the file loaded.
It still puzzles me why it "can't find the file" when clearly, clicking "Find Now" after I've typed in ksln shows Salina Municipal.
So ADE found it, why has it lost it again?
That's weird. I just repeated this on my installation and the airport opened straight away without error. Selecting stock airports has not changed in version 1.79. The only thing I can think of is that this error arises if the path to the sim is not correct, Or perhaps it is not available for some reason. ADE finds the airport you select using a stock index which is created from the stock installation. To load the airport it adds the path to the sim scenery file to the index data which is the sub folder inside the Scenery main folder.
I think you've nailed it.
"... error arises if the path to the sim is not correct ..."
I compared the ini files in both installations and found that FsPath in 1.78 has a trailing backslash, 1,79 doesn't.
I've added it to 1.79 and opened half a dozen random airports (not that random , all Kansas, the current project) and not had a problem.
I'll keep my fingers crossed.