[13:13:35 INFO]: Lurreisper issued server command: /. $
[13:13:35 ERROR]: Could not pass event PlayerCommandPreprocessEvent to SimpleClans v2.7.11
org.bukkit.event.EventException
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:310) ~[spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:502) [spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:487) [spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at net.minecraft.server.v1_8_R3.PlayerConnection.handleCommand(PlayerConnection.java:1154) [spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at net.minecraft.server.v1_8_R3.PlayerConnection.a(PlayerConnection.java:997) [spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at net.minecraft.server.v1_8_R3.PacketPlayInChat.a(PacketPlayInChat.java:45) [spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at net.minecraft.server.v1_8_R3.PacketPlayInChat.a(PacketPlayInChat.java:1) [spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at net.minecraft.server.v1_8_R3.PlayerConnectionUtils$1.run(SourceFile:13) [spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [?:1.8.0_181]
at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.8.0_181]
at net.minecraft.server.v1_8_R3.SystemUtils.a(SourceFile:44) [spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:715) [spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:374) [spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:654) [spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:557) [spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_181]
Caused by: java.lang.IllegalArgumentException: Illegal group reference: group index is missing
at java.util.regex.Matcher.appendReplacement(Unknown Source) ~[?:1.8.0_181]
at java.util.regex.Matcher.replaceAll(Unknown Source) ~[?:1.8.0_181]
at java.lang.String.replaceAll(Unknown Source) ~[?:1.8.0_181]
at net.sacredlabyrinth.phaed.simpleclans.Helper.formatClanChat(Helper.java:665) ~[?:?]
at net.sacredlabyrinth.phaed.simpleclans.managers.ClanManager.processClanChat(ClanManager.java:1157) ~[?:?]
at net.sacredlabyrinth.phaed.simpleclans.managers.ClanManager.processClanChat(ClanManager.java:1094) ~[?:?]
at net.sacredlabyrinth.phaed.simpleclans.listeners.SCPlayerListener.onPlayerCommandPreprocess(SCPlayerListener.java:94) ~[?:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_181]
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_181]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_181]
at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_181]
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:306) ~[spigot-1.8.8-R0.1-SNAPSHOT-latest.jar:git-Spigot-db6de12-18fbb24]
... 16 more

Test this version, please: https://1drv.ms/u/s!Av2G_9O8Vhlhptp11P3noTf8HvE59w
Let me know if it's fixed!

It worked =D