As you know, Calibre is a powerful tool that allows you to easily manage your e-book library. It also allows you to back up the e-books that you buy online and to transfer them to other devices when your e-book reader is out-of-order.
Sometimes the problem is that e-book formats evolve rapidly and new versions have been “recently”created. For this reason I personally suggest to update Calibre very often because new version have, obviously, the most updated plugins and consequently support new formats.
The Calibre website has a good download section where you find easy instructions to update your e-book reader on almost any OS. In my experience, usually you spend less than 6-7 minutes to update Calibre and the advantages you have worth the time you spend.
Moreover, if you have problems to read an e-book on the last version of Calibre, check the file format (in my case was .azw3), launch Calibre and go in Preferences → Behaviour. Then, be sure that the file format you are trying to open/read is correctly activated into the list you find there. Enjoy your reading!