Please be sure you have upgraded either to Project Professional 2016 or are running the subscription model and are actively updating to at least the deferred channel. Although RTM is acceptable for Project Professional 2016 you should consider patching to a more recent update. If you are still running Project 2013 then you will not be able to connect to Project Online once this deadline passes (June 30, 2017). As mentioned recently for the site creation changes – the Message Center is the place to learn about this and other changes. To read more about this click here.