Check Call Restrictions - 34

There is a cell tower nearby, but your cell phone network provider is unwilling to pay for that tower to carry your calls. However, federal law requires that any cell phone be able to call 911 at all times. Thus, bullshit like which towers your cell phone provider will and won't pay for access to aren't permitted to deny you the ability to make any call whatsoever. Thus, the phone cannot simply tell you that you have no signal, because that isn't true: You can still call 911 because you do have a signal. However, your network provider doesn't want to pay for any calls through that tower, and so if you attempt to make any call that it isn't required by federal law to permit, your phone will not allow it. As for why this error message is so vague, one can only wonder. It probably has something to do with your network provider not wanting you to know what a bunch of douches they are and hoping that if you only see this message occasionally then you won't put too much effort into figuring out what the problem is.

TL;DR version: Your cell phone provider sucks.