Error sending 'new' text messages
 

This is just a minor problem, but it is annoying me. I am texting people who I've texted before and who are in my contacts, but for some reason I get the following message popup whenever I send a text message created from 'New'. I don't get it when I 'Reply' to an existing message.

Cannot recognize one or more recipients or the address is not valid. Would you like to send the message anyway?

I hit the 'Yes' button and the message goes out fine - but why do I get the message to start with?