Sentry Error please report this error [see console]

[BeniBeast]

[20:11:15 WARN]: at net.minecraft.server.v1_9_R1.PlayerConnection.a(PlayerConnection.java:1158) [20:11:15 WARN]: at net.minecraft.server.v1_9_R1.PacketPlayInChat.a(SourceFile:37) [20:11:15 WARN]: at net.minecraft.server.v1_9_R1.PacketPlayInChat.a(SourceFile:9) [20:11:15 WARN]: at net.minecraft.server.v1_9_R1.PlayerConnectionUtils$1.run(SourceFile:13) [20:11:15 WARN]: at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [20:11:15 WARN]: at java.util.concurrent.FutureTask.run(Unknown Source) [20:11:15 WARN]: at net.minecraft.server.v1_9_R1.SystemUtils.a(SourceFile:45) [20:11:15 WARN]: at net.minecraft.server.v1_9_R1.MinecraftServer.D(MinecraftServer.java:679) [20:11:15 WARN]: at net.minecraft.server.v1_9_R1.DedicatedServer.D(DedicatedServer.java:361) [20:11:15 WARN]: at net.minecraft.server.v1_9_R1.MinecraftServer.C(MinecraftServer.java:635) [20:11:15 WARN]: at net.minecraft.server.v1_9_R1.MinecraftServer.run(MinecraftServer.java:539) [20:11:15 WARN]: at java.lang.Thread.run(Unknown Source) [20:11:15 WARN]: Caused by: java.lang.ClassNotFoundException: net.minecraft.server.v1_7_R3.World [20:11:15 WARN]: at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:67) [20:11:15 WARN]: at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:62) [20:11:15 WARN]: at java.lang.ClassLoader.loadClass(Unknown Source) [20:11:15 WARN]: at java.lang.ClassLoader.loadClass(Unknown Source) [20:11:15 WARN]: ... 30 more

[mcmonkey4eva]

You're using Sentry for 1.7.10 on a 1.9 server. See here for a newer plugin compat with 1.9: https://github.com/mcmonkey4eva/Sentinel/blob/master/README.md