I'm probably stupid but..

[root@vps25108 SRBungee]# java -Xms500M -Xmx600M -jar BungeeCord.jar
Exception in thread "main" java.lang.NoClassDefFoundError: net.md_5.bungee.Bootstrap
   at java.lang.Class.initializeClass(libgcj.so.10)
Caused by: java.lang.ClassFormatError: net.md_5.bungee.api.ProxyServer (unrecognized class file version)
   at java.lang.VMClassLoader.defineClass(libgcj.so.10)
   at java.lang.ClassLoader.defineClass(libgcj.so.10)
   at...