It's possible that the person you're PM'ing has not cleaned / emptied out his or her inbox- then they cannot receive new messages.
I didn't even notice the change and got used to it in a day. I love the Chat the way it is, less spam. But it has become awfully unpopular
PMing was difficult at first, whenever I try to PM my friend, it always says:
"this recipent cannot recieve any new messages"
or something like that. Wierd. It still happens.
I think you can try commenting on their profile though... tell them to clean out their inbox and try again. :]