SEVERE: Could not load plugins/mcsl-plugin.jar in plugins: null
org.bukkit.plugin.InvalidPluginException
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.                                      java:70)
        at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager                                      .java:115)
        at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManage                                      r.java:80)
        at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:43)
        at net.minecraft.server.MinecraftServer.e(MinecraftServer.java:153)
        at net.minecraft.server.MinecraftServer.c(MinecraftServer.java:140)
        at net.minecraft.server.MinecraftServer.d(MinecraftServer.java:104)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:177)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:512)
Caused by: java.util.zip.ZipException: error in opening zip file
        at java.util.zip.ZipFile.open(Native Method)
        at java.util.zip.ZipFile.<init>(ZipFile.java:131)
        at java.util.jar.JarFile.<init>(JarFile.java:150)
        at java.util.jar.JarFile.<init>(JarFile.java:114)
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.                                      java:57)
        ... 8 more