If your version of neXt was purchased through Apple's App Store and doesn't start anymore:

All 3rd party programs which were purchased in Apple's App Store have the same problem as a required certificate from Apple expired as has been replaced (12-11-2015). You will need to manually delete neXt from your computer and re-download it from the Apple AppStore from your "Purchased" tab to remediate this issue.

So, please report this bug to Apple.

Further informations: http://www.macrumors.com/2015/11/12/mac-...receipts-issue/

Now it works. Delete neXt from your computer and re-download it from the Apple AppStore from your "Purchased" tab to remediate this issue. I'm on OSX 10.11.1. They have fixed the problem.