Moving to InDesign forum
It could be because InDesign CS5.5 is not supported under El Capitan. There is no support provided for that version anymore so I'm afraid you're on your own trying to solve it. The only real answer is to upgrade to a Creative Cloud subscription.
did you al ready find the time to have a look at the idml-file? Do you think the problem is file-related or could it be there is an interaction problem in-between CS5.5 and CC?
Thank you in advance,