1. If you're referring to iMessages, then it could be that they have blocked you or have turned iMessage off on their devices.
2. It's also possible that you be experiencing internet-related problems whether via your ISP or your wireless carrier.
3. If "just started happening" means moments ago, it's possible that Apple could be experiencing iMessage-related problems in your area that is only affecting a miniscule amount of users.
4. If you're referring to SMS messages, there could be issues with your wireless carrier.
Anyway, try rebooting your device and/or going to Settings - General - Reset and then select "Reset Network Settings" to see if that helps.
11-30-2014 03:04 PM