The message can be confusing. What you actually have to do is upgrade InDesign.
Oooh really ?
Hmmm.. That's pitty...
Yes. If a file is saved in InDesign, no OLDER version of InDesign can open it. There is a special way to export a portable file if you want to try and recover a file in an older version, though results may not be perfect (especially if new features were used).