Bypass pre-set slots, some shared host's do this so here is a simple bypass.

SlotsBypass.java

package com.colt.SlotsBypass;

import org.bukkit.Bukkit;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.EventPriority;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerLoginEvent;
import org.bukkit.event.server.ServerListPingEvent;
import org.bukkit.plugin.java.JavaPlugin;

public class SlotsBypass extends JavaPlugin implements Listener{
	
	String permission = getConfig().getString("permission");
	int maxplayers = getConfig().getInt("max-players");
	
	@Override
	public void onEnable() {
		Bukkit.getServer().getPluginManager().registerEvents(this, this);
		saveDefaultConfig();
	}

	@EventHandler(priority = EventPriority.NORMAL)
	public void playerLogin(PlayerLoginEvent e) {
		Player p = e.getPlayer();
		if(e.getResult() == PlayerLoginEvent.Result.KICK_FULL && !(Bukkit.getOnlinePlayers().size() > maxplayers &&
			p.hasPermission(permission))) {
				e.setResult(PlayerLoginEvent.Result.ALLOWED);
		}
	}
	
	@EventHandler
	public void ping(ServerListPingEvent e){
		e.setMaxPlayers(maxplayers);
	}
}