The TeamSpeak server of CubeCraft needs your Teamspeak identity (see below) be more secure, but yours isn't, so just click start, it won't do anything wrong to you. You should make a backup first.
What is an identity? An identity in TeamSpeak is a file that contains data about you using TeamSpeak, servers you entered, your name... That's also used by the servers to assign you the rank and permissions you should have.
Hope that helped you.