I've been having this problem for a long time. I can't read my messages here. The ones in the Inbox (I can see the "Sent" messages).
So, the only way I can see the messages who users send me is through my email. They don't appear here. That's why I can't reply them either. Instead, I have to create a new message.
Anyone has a clue on why this is happening to me?
(The last message I have in my Inbox is from 2009 :S)