Texts Keep Failing


Android Question

I have a Samsung Galaxy Note 4. Previously has an iPhone 4S. I love my Note 4, but for some reason texts to only one specific number keep failing. All other texts go out. Except for this contact. I've tried restarting the phone, clearing out the conversation history. It's really frustrating that the number I'm trying to text happens to be my boss -_- HELP! What can I do to fix this!