Reply To: "out of memory" error

It is extremely hard to debut problems like this. It’s always good to try:
a) Rebuild your InDesign preference files ( https://creativepro.com/resources/faq )
b) Restart the computer
c) Log in to your computer using a different account (like a guest account or some other account)

Often one of those things helps.

As for supporting CS6 or earlier versions of the program: I feel your pain, but one of the whole points of new versions of software is that it keeps up with changes in operating systems, right? Adobe can’t go back and make CS5 and CS4 and CS and InDesign 2 and so on keep working in El Capitan. It just isn’t feasible.