PTLive needs everyone to be working with the same project data. If you haven’t all done a couple rounds of S/R before starting PTLive, it needs to basically do the S/R for you to make sure you all are working with exactly the same project data. That’s what it means when it talks about synchronization - getting all users to have the same data before starting. Because of that, it can take a while (I’m not sure how long you waited).
If it seems to be getting stuck on that, then you can try manually doing two rounds of S/R with everyone and try again.
EDIT: The “versions” refers to how many different copies of the project data there are, that are different from each other.