Eclipse不会导出插件

Question

Eclipse不想导出我的minecraft插件，并显示以下错误

JAR creation failed. See details for additional information.
  Class files on classpath not found or not accessible for: 'TeraMC - Skyblock/src/de/cha0s/skyblock/commands/WarpCommand.java'
  Class files on classpath not found or not accessible for: 'TeraMC - Skyblock/src/de/cha0s/skyblock/constructor/ItemManager.java'

我已经删除了WarpCommand类和ItemManager类。但是我需要它们，没有它们，我无法将玩家传送到Warplocations。

ItemManager: public class ItemManager {

    public static void createInventoryItem(Player p, Material material, String displayName, Integer slot, Inventory inv) {
        ItemStack i = new ItemStack(material);
        ItemMeta im = i.getItemMeta();
        im.setDisplayName(displayName);
        i.setItemMeta(im);
        inv.setItem(slot, i);
        p.openInventory(inv);
    }

    public static void createItem(Player p, Material material, String displayName, Integer slot, Enchantment ench, Integer level, Enchantment ench2, Integer level2, Boolean hideEnchants, Boolean unbreakable) {
        ItemStack i = new ItemStack(material);
        ItemMeta im = i.getItemMeta();
        im.setDisplayName(displayName);
        if(ench != null && level != null) {
            im.addEnchant(ench, level, true);
        } if(ench2 != null && level2 != null) {
            im.addEnchant(ench2, level2, true);
        } if(hideEnchants == true) {
            im.addItemFlags(ItemFlag.HIDE_ENCHANTS);
        } if(unbreakable == true) {
            im.spigot().setUnbreakable(true);
        }
        i.setItemMeta(im);
        p.getInventory().setItem(slot, i);
    }


WarpCommand: public class WarpCommand implements CommandExecutor {

    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {

        if(sender instanceof Player) {
            Player p = (Player) sender;
            Inventory i = Bukkit.createInventory(null, 9*1, "§6§lTeleportierungsmenü");

            ItemManager.createInventoryItem(p, Material.DIAMOND_SWORD, "§e§lBossarena", 0, i);
            ItemManager.createInventoryItem(p, Material.DIAMOND, "§e§lTutorials", 2, i);
            ItemManager.createInventoryItem(p, Material.NETHER_STAR, "§e§lSpawn", 4, i);
            ItemManager.createInventoryItem(p, Material.ENCHANTED_BOOK, "§e§lVerzauberungsmechaniker", 6, i);
            ItemManager.createInventoryItem(p, Material.GOLD_NUGGET, "§e§lShop", 8, i);
        }
        return false;
    }

我期望Eclipse导出插件，但我唯一得到的是上面的错误消息