On skyblock I cant leave my island... it always says: An internal error occurred while trying to perform this command
If you changed your name, change it back to your first name. It will restart the island I believe, but it will let you play.
They have added this to the "To-Do List" because people (not as much now) get the error when starting or leaving. It was real bad a month or two ago, nobody could start an island for like 3 days!
This stopped happening to me after I changed my name, though you shouldn't have to change anything for this to work. :/