Could be my fault but this message shows up like every second.

[01:24:57] [Server thread/WARN]: [Quester] Task #1350447 for Quester v0.6.3.6 generated an exception
java.lang.NoSuchMethodError: org.bukkit.Server.getOnlinePlayers()[Lorg/bukkit/entity/Player;
at com.gmail.molnardad.quester.listeners.PositionListener.run(PositionListener.java:28) ~[?:?]
at org.bukkit.craftbukkit.v1_11_R1.scheduler.CraftTask.run(CraftTask.java:71) ~[spigotmc-1.11.2-R0.1.jar:git-Spigot-625bc00-b5f7b6d]
at org.bukkit.craftbukkit.v1_11_R1.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:353) [spigotmc-1.11.2-R0.1.jar:git-Spigot-625bc00-b5f7b6d]
at net.minecraft.server.v1_11_R1.MinecraftServer.D(MinecraftServer.java:738) [spigotmc-1.11.2-R0.1.jar:git-Spigot-625bc00-b5f7b6d]
at net.minecraft.server.v1_11_R1.DedicatedServer.D(DedicatedServer.java:399) [spigotmc-1.11.2-R0.1.jar:git-Spigot-625bc00-b5f7b6d]
at net.minecraft.server.v1_11_R1.MinecraftServer.C(MinecraftServer.java:678) [spigotmc-1.11.2-R0.1.jar:git-Spigot-625bc00-b5f7b6d]
at net.minecraft.server.v1_11_R1.MinecraftServer.run(MinecraftServer.java:576) [spigotmc-1.11.2-R0.1.jar:git-Spigot-625bc00-b5f7b6d]
at java.lang.Thread.run(Thread.java:745) [?:1.7.0_101] # #66

It's spamming my console and I don't get what it says sooo...

I have only one quest right now that is called Retrieve Joshua's pickaxe, it basicly requires you to bring an NPC an item.

Thanks in advance.