Scheduler Error

Can someone help how to fix this?

 

public function onEnable() {
$this->getServer()->getPluginManager()->registerEvents($this, $this);
@mkdir($this->getDataFolder());
@mkdir($this->getDataFolder() . "/maps");
$this->saveDefaultConfig();
$this->reloadConfig();
$this->getLogger()->info("§aTNTRun by §6CraftYourBukkit §aloaded.");
$this->prefix = $this->getConfig()->get("prefix");
$this->getServer()->getScheduler()->scheduleRepeatingTask(new GameSender($this), 20);
$this->getServer()->getScheduler()->scheduleRepeatingTask(new RefreshSigns($this), 20);
foreach ($this->getConfig()->getNested("arenas") as $a) {
if (!$this->getServer()->getLevelByName($a["name"]) instanceof Level) {
$this->deleteDirectory($this->getServer()->getDataPath() . "/worlds/" . $a["name"]);
$this->copymap($this->getDataFolder() . "/maps/" . $a["name"], $this->getServer()->getDataPath() . "/worlds/" . $a["name"]);
$this->getServer()->loadLevel($a["name"]);
} else {
$this->getServer()->unloadLevel($this->getServer()->getLevelByName($a["name"]));
$this->deleteDirectory($this->getServer()->getDataPath() . "/worlds/" . $a["name"]);
$this->copymap($this->getDataFolder() . "/maps/" . $a["name"], $this->getServer()->getDataPath() . "/worlds/" . $a["name"]);
$this->getServer()->loadLevel($a["name"]);
}
}
}