Good afternoon stoner10!
I apologize for the delay for this response. Are you still experiencing issues with sending messages? Does this happen often? In some cases, you may get this error when you're recieving a message at the exact same time, or possibly an incoming call. Also, are you using default messaging application, or 3rd party application? Please try using default application if you're not already. You can also delete message threads and re-try sending again. Please keep us posted so we can better understand and assist.
Follow us on Twitter @VZWSupport