In minecraft server 1.7.10 and forge10.13.4.1558, SlashBlade-mc1.7.10-r77 work well but SlashBlade-mc1.7.10-r85,r86 doesn't.

I can't resolve this problem. Please help me.

Following text is the crash log.

---- Minecraft Crash Report ----
// Who set us up the TNT?

Time: 9/28/16 3:58 AM
Description: Exception in server tick loop

cpw.mods.fml.common.LoaderException: java.lang.ClassNotFoundException: mods.flammpfeil.slashblade.SlashBlade
at cpw.mods.fml.common.LoadController.transition(LoadController.java:163)
at cpw.mods.fml.common.Loader.loadMods(Loader.java:544)
at cpw.mods.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:87)
at cpw.mods.fml.common.FMLCommonHandler.onServerStart(FMLCommonHandler.java:314)
at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:117)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:387)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)
Caused by: java.lang.ClassNotFoundException: mods.flammpfeil.slashblade.SlashBlade
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
at cpw.mods.fml.common.ModClassLoader.loadClass(ModClassLoader.java:58)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:278)
at cpw.mods.fml.common.FMLModContainer.constructMod(FMLModContainer.java:440)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.google.common.eventbus.EventSubscriber.handleEvent(EventSubscriber.java:74)
at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322)
at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304)
at com.google.common.eventbus.EventBus.post(EventBus.java:275)
at cpw.mods.fml.common.LoadController.sendEventToModContainer(LoadController.java:212)
at cpw.mods.fml.common.LoadController.propogateStateMessage(LoadController.java:190)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.google.common.eventbus.EventSubscriber.handleEvent(EventSubscriber.java:74)
at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322)
at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304)
at com.google.common.eventbus.EventBus.post(EventBus.java:275)
at cpw.mods.fml.common.LoadController.distributeStateMessage(LoadController.java:119)
at cpw.mods.fml.common.Loader.loadMods(Loader.java:513)
... 5 more
Caused by: java.lang.UnsupportedClassVersionError: mods/flammpfeil/slashblade/SlashBlade : Unsupported major.minor version 52.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:803)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:182)
... 33 more

A detailed walkthrough of the error, its code path and all known details is as follows:

-- System Details --
Details:
Minecraft Version: 1.7.10
Operating System: Linux (amd64) version 3.19.0-66-generic
Java Version: 1.7.0_101, Oracle Corporation
Java VM Version: OpenJDK 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 961973896 bytes (917 MB) / 1029701632 bytes (982 MB) up to 1908932608 bytes (1820 MB)
JVM Flags: 2 total; -Xms1024M -Xmx2048M
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP v9.05 FML v7.10.99.99 Minecraft Forge 10.13.4.1558 4 mods loaded, 4 mods active
States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
UC mcp{9.05} Minecraft Coder Pack
UC FML{7.10.99.99} Forge Mod Loader
UC Forge{10.13.4.1558} Minecraft Forge
UE flammpfeil.slashblade{mc1.7.10-r85} SlashBlade
Profiler Position: N/A (disabled)
Is Modded: Definitely; Server brand changed to 'fml,forge'
Type: Dedicated Server (map_server.txt)

java8 or later is required.

Since the development environment was in the virus damage, our policy is not carried out the construction of the old java.

I changed java7 to java8, and it works. Thank you.