You state "Index/Table of contents" – these are two different things. The index goes at the back of the book and the TOC at the front.
Did you create the TOC using InDesign's TOC creation facility?
You need to have two TOCs – an external one and an HTML one – presumable you're having problems with the HTML one.
What does it state if you use the IDPF validator: EPUB Validator (beta)
How are you viewing your ePub?
I've moved your question to the InDesign EPUB forum.
Ah sorry, I use the Swedish version and don't know what Innehållsförteckning translates to in the English version.. But it is most likely Table of contents. Yes I used the TOC creation facility, not that familiar with this program though. The validator doesn't state anything about the TOC from what I can see. I view the ePub in iBooks...
Thank you I didn't know there was one!