Bukkit

What version of the product are you using?
3.3.10

Do you have an error log of what happened?

[20:12:43] [Craft Scheduler Thread - 4/WARN]: Exception in thread "Craft Scheduler Thread - 4"
[20:12:43] [Craft Scheduler Thread - 4/WARN]: org.apache.commons.lang.UnhandledException: Plugin AuthMe v5.0-SNAPSHOT generated an exception while executing task 37
    at org.bukkit.craftbukkit.v1_9_R1.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NoSuchMethodError: org.bukkit.Server.getOnlinePlayers()[Lorg/bukkit/entity/Player;
    at fr.xephi.authme.Metrics.postPlugin(Metrics.java:335)
    at fr.xephi.authme.Metrics.access$400(Metrics.java:57)
    at fr.xephi.authme.Metrics$1.run(Metrics.java:223)
    at org.bukkit.craftbukkit.v1_9_R1.scheduler.CraftTask.run(CraftTask.java:71)
    at org.bukkit.craftbukkit.v1_9_R1.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
    ... 3 more
Please provide any additional information below.