I got this by running the plugin for the first time

[dungeonmaster372]

[06:34:01] [Server thread/ERROR] [FML/]: Caught exception from Core java.lang.NoClassDefFoundError: org/spongepowered/api/service/ProviderExistsException at java.lang.Class.forName0(Native Method) ~[?:1.8.0_73] at java.lang.Class.forName(Unknown Source) ~[?:1.8.0_73] at org.spongepowered.mod.plugin.SpongeModPluginContainer.constructMod(SpongeModPluginContainer.java:89) ~[spongeforge-1.8.9-1732-3.1.0-BETA-1141.jar:1.8.9-1732-3.1.0-BETA-1141] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_73] at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_73] at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_73] at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_73] at com.google.common.eventbus.EventSubscriber.handleEvent(EventSubscriber.java:74) ~[minecraft_server.1.8.9.jar:?] at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47) ~[minecraft_server.1.8.9.jar:?] at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322) ~[minecraft_server.1.8.9.jar:?] at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304) ~[minecraft_server.1.8.9.jar:?] at com.google.common.eventbus.EventBus.post(EventBus.java:275) ~[minecraft_server.1.8.9.jar:?] at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:211) ~[LoadController.class:?] at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:189) ~[LoadController.class:?] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_73] at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_73] at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_73] at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_73] at com.google.common.eventbus.EventSubscriber.handleEvent(EventSubscriber.java:74) ~[minecraft_server.1.8.9.jar:?] at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47) ~[minecraft_server.1.8.9.jar:?] at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322) ~[minecraft_server.1.8.9.jar:?] at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304) ~[minecraft_server.1.8.9.jar:?] at com.google.common.eventbus.EventBus.post(EventBus.java:275) ~[minecraft_server.1.8.9.jar:?] at net.minecraftforge.fml.common.LoadController.onPost(LoadController.java:53) ~[LoadController.class:?] at net.minecraftforge.fml.common.LoadController.distributeStateMessage(LoadController.java:118) [LoadController.class:?] at net.minecraftforge.fml.common.Loader.loadMods(Loader.java:512) [Loader.class:?] at net.minecraftforge.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:87) [FMLServerHandler.class:?] at net.minecraftforge.fml.common.FMLCommonHandler.onServerStart(FMLCommonHandler.java:320) [FMLCommonHandler.class:?] at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:112) [ko.class:?] at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:441) [MinecraftServer.class:?] at java.lang.Thread.run(Unknown Source) [?:1.8.0_73] Caused by: java.lang.ClassNotFoundException: org.spongepowered.api.service.ProviderExistsException at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191) ~[launchwrapper-1.12.jar:?] at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_73] at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_73] ... 31 more Caused by: java.lang.NullPointerException at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:182) ~[launchwrapper-1.12.jar:?] at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_73] at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_73] ... 31 more