I have had this problem 2 it means 4 people were in the dungeon.Then i guess one left.Well the game still acts like like there are 4 people in there evan though there is only 3.You have too wait 30 minutes before it stops doing this.
They need to fix that. I've had that problem and if you have to port out to get energy sometimes you can't get back in. That happened to a friend of mine when we were battling Malistare. We decided to turn ports off and flee when we had too and then turn ports back on so we could get back in the dungeon.
One thing to keep in mind is if somebody leaves a dungeon by porting, it keeps you as active in it. So if a friend leaves a dungeon by porting to the commons, or to their house, the system thinks they are coming back so it saves their spot for the "timeout" duration. That's how you can get potions if you need them and rejoin the fight without starting the dungeon over. So if a friend leaves and they don't log out to character selection, or flee the dungeon, nobody can take their place. Hope that helps. I used to get super annoyed by that error till I figured all that out. I think it does glitch from time to time though as well.
What dungeon is it? There are some dungeons that are closed, which means you can't port into them, you have to go in on the sigil at the same time....
There is one like this in Crystal Grove, Grand Chasm, Necropolis and probably a few others I can't remember.
It can happen on any dungeon that allows others in with you. There are indeed a couple you need to join at the same time, but that isn't what is being discussed here.
. My friend says its not full in the dungeon. Why wont it let me in?