No answer? Just ran into the same problem here running the latest stable build of MC19.
* Don't have many ISOs which is why I haven't noticed till now. I'm trying to get back into my guitar training ... new year resolution and all that. I do know they worked perfectly last time I made (and abandoned) the same resolution. ;-}
UPDATE > >
I usually keep my server offline as it's mostly for audio playback. Went online to ask this question, and next time I tried firing one of the ISO's I got an "INSTALLING REQUIRED COMPONENTS" message. Working fine now.
* Be nice if we could get MC to give us an "I NEED MORE COMPONENTS - GO ONLINE, DUMMY!" message instead of the one I got ... (harumph)