Could not initialize class!

This is the Only Thing that makes server to Crash!!! Help!
[18:00:26] [Server thread/ERROR]: Encountered an unexpected exception
java.lang.NoClassDefFoundError: Could not initialize class net.minecraft.server.v1_7_R1.CrashReport
at net.minecraft.server.v1_7_R1.MinecraftServer.u(MinecraftServer.java:638) ~[spigot.jar:git-Spigot-1223]
at net.minecraft.server.v1_7_R1.DedicatedServer.u(DedicatedServer.java:273) ~[spigot.jar:git-Spigot-1223]
at...

Could not initialize class!