In my opinion the safest conversion of legacy files is always to export from the original version to .idml, then open that in the new version.
I thought that was for going backwards in application versions, i need to suggest that for going forwards too?
I would not do it except an error comes up, because many unwanted changes in the file appear with IDML export.
But what is the content in your file?
- Did you embed graphics?
- What kind or type of graphics did you use?
- What is the size of the file?
- Are all used fonts ok?
doing the .idml export eliminates a lot of unpleasant surprises, like unexpected reflow (it will all recompose when you open the .idml so you won't get caught by surprise when stories recompose because you clicked in them) and failure to output after you've spent three weeks editing.