Whenever I try to run Minecraft on my VPS, I get the error below. I am using CentOS, newest Java (reinstalled), and the newest version of the Minecraft Server package. The weird part is, it was running perfectly for more that an hour and a half with 20+ people on it, I shut it down so I could put a new map on, then when I tryed to restart it, I got the error below.

Exception in thread "main" java.lang.NoClassDefFoundError: com/mojang/minecraft/server/MinecraftServer
Caused by: java.lang.ClassNotFoundException: com.mojang.minecraft.server.MinecraftServer
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
Could not find the main class: com.mojang.minecraft.server.MinecraftServer. Program will exit.