Twitter problem

If you aren't following mutually someone, or they are set to private, you can't. Do this instead:

@whatevertheirTwitterhandleis then write your message (140 characters max, as always. Plus this is public).

That is why you need to have a strategy to make them follow you. So you can follow each other and be able to send a direct message. I'm not sure if this was already with Twitter or it was updated resulting to "DM NOT ALLOWED" unless you're following each other.