We're going to need a lot more info to help you with this.
Where are you getting this message? Is it one specific app or everything? Phone make, model, Android version (assuming that's what you'd referring to, since this is an Android forum)? Are you trying to connect via mobile data or Wi-Fi? If Wi-Fi, is it your own service or someone else's? How were you able to post this question if you're not able to get online?
You'll need to register an account to reply to this thread and answer those questions. Otherwise, the solution could be a thousand different possibilities.