Thank you for that; I've just come back to b4i after some months, and with a new test device (a 5, on latest iOS). I've spent all afternoon recreating profiles and certificates, and rebooting, all with the same result - "Cannot connect"
Finally, I found this thread, and your solution has worked. (Also, I'm even less impressed than before with Apple's UX; a message about certificate trust would at least have pointed in the right direction, rather than just bleating "Cannot connect.")