Bukkit

[10:54:21 WARN]: [Wizards] Task #52 for Wizards v1.5.2 generated an exception
java.lang.NoSuchMethodError: org.bukkit.Server.getOnlinePlayers()[Lorg/bukkit/entity/Player;
at com.gmail.josemanuelgassin.Wizards._Wizards.actualizarManaExp(_Wizards.java:215) ~[?:?]
at com.gmail.josemanuelgassin.Wizards._Wizards$2.run(_Wizards.java:209) ~[?:?]
at org.bukkit.craftbukkit.v1_11_R1.scheduler.CraftTask.run(CraftTask.java:71) ~[craftbukkit.jar:git-Spigot-b605b31-f4822eb]
at org.bukkit.craftbukkit.v1_11_R1.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:353) [craftbukkit.jar:git-Spigot-b605b31-f4822eb]
at net.minecraft.server.v1_11_R1.MinecraftServer.D(MinecraftServer.java:738) [craftbukkit.jar:git-Spigot-b605b31-f4822eb]
at net.minecraft.server.v1_11_R1.DedicatedServer.D(DedicatedServer.java:399) [craftbukkit.jar:git-Spigot-b605b31-f4822eb]
at net.minecraft.server.v1_11_R1.MinecraftServer.C(MinecraftServer.java:678) [craftbukkit.jar:git-Spigot-b605b31-f4822eb]
at net.minecraft.server.v1_11_R1.MinecraftServer.run(MinecraftServer.java:576) [craftbukkit.jar:git-Spigot-b605b31-f4822eb]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_121]