If you try again in 15-30 minutes it should work, if not that usually means they haven't logged on in a really long time.
If the server has done a normal reset recently it's probably that, it does the same for me too. Just give it a bit of time and try again.
15-30 minutes after your last try. Keep in mind that if the user has been inactive for a while, it might not work permanently.
I had this but then i thought about and it's either, A. Your friend hasn't been on in a while B. The Sever has done a reset Hope this helps <-------- what i thought had happen, Maybe i am incorrect