Are you able to try another Bluetooth connection, such as a headset? If you get the same message, there may be a hardware problem which would require a repair. Before you go down that route, though, there are a couple of things you can try. Firstly, tap the little overlapping-page icon to the riht of the home key and close all recent apps. This will free up some resources and may fix it. If not, try a factory reset (back up your content and make sure your contacts and calendar are fully sync'd first).
Did this happen after a firmware update? In that case, the factory reset may help, but it's also possible that your Bluetooth is no longer compatible with the software in the car. Car software is often flaky and/or out of date, though a dealer may have an update which will make it work again.
