The following was more or less discovered by the user "The Pragmatic". The problem is some users seem to have 2 (or more!) different names. Their initial name, and their current name. When you click on the button to send someone a message, it populates the form with their current name; HOWEVER, if you do not use the initial name the message will fail.

So if their initial name is different from their current name, using the button to populate the name field will fail when you try to send it. In this case you need to manually type in their initial name.

The next logical question is: how can I tell what someone's initial name is?

Answer: I have no fucking idea. The only reason I know it works is I've had someone tell me their initial name and it fixed the problem.

One solution is to have them message you (assuming you don't have this 2 name problem yourself). Once you have a conversation going, you can use the reply option to message them successfully.

/e I should add that all of this is just a guess, from examining the black box that is the atheistrepublic.com we don't have any inside info, so this could be wrong I suppose.