"Ooops players it not joinable anymore"
So when its gonna get fixed?
You can set party to open, restricted to friends, guildmates but no matter "how open" is it people have this error when they try to join. Of course you are in party lobby, floor 0 and they cant join because of "oops players is no longer joinable" error but when you send them invite they can join without problems.
This occurs when you join a lobby of a mission you've already completed, if you haven't completed the mission then you can join said lobby with no problems.
This is a side effect of the Dark Harvest Festival "Punkin" exploit that was fixed, so perhaps whatever was done needs to be reversed again.
Thankfully a lot of members in my Guild (To The Death) aren't at the point of farming the Vana missions so it's not too much of a problem for them, but of course more of a pain when I want to join a Vana party (as I've already completed it myself).
=)