It's most likely that the map was at full population at the time(s) you were trying to enter. You can come on the forum here and check the map populations by holding your arrow over the right side of the forum. Were you maybe trying to enter on a character that is in Fluorite at the time? If so that could be why because currently it is very crowded. Consider using the character reset option at the top right of the forum if any of your characters are stuck on that map:
Or you can always just keep trying to enter, play on a less crowded map, or just be patient and wait it out until the population goes down a bit again. Also remember that the server has been having some trouble for a while now so it could be a server issue. Just give it some time before you try entering again.
Hope that helps Jynx