I have been having this issue for the last two weeks, too. I've rebooted my phone a number of times, reset my network settings 3 times, reset my entire phone once, removed my Sim card twice... I've feel like I've done everything I can based on the troubleshooting I've found online. Seems like an aweful lot of people are having this problem. Constanting getting the "not delivered" when people are actually getting the message. I'll send it as a text message becuase it says not delivered and they will get it twice. Same thing happenes on their end and I'll get stuff twice. I'll send something once and the other person gets it multiple times. Just happens with pictures, and just over the last two weeks or so. This is happening with several different contacts, all of us have updated software. One has an iphone 4S, a couple of us have a 5 and the others all have the 5S. It's driving us all CRAZY.