I have the same issue. But only with one number. The first attempt at SMS I didn't provide the area code and received the message to provide area code. I then provided the area code but continued to get the message.
I then removed all SMS threads, removed the contact and readded the contact with the area code. I was then able to send a few SMS messages before the issue reoccurred. So, now I have a work around but continue to have to repeat the process every so often. It has become a real pain because the contact is my daughter, who I text with fairly often.