Won't load plugins?

Hi, so I'm pretty new to bukkit (only a month) and I just cannot seem to get something working. I am using a mac Desktop, dedicated server. Anyway my server works great everything is fine except for one thing. My plugins will not work. When I open a server my terminal says something like this.

07.02.2011 20:11:07 org.bukkit.plugin.SimplePluginManager loadPlugins SEVERE: Could not load plugins/DropChest.jar in plugins: null org.bukkit.plugin.InvalidPluginException at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:78) at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:117) at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:82) at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:48) at net.minecraft.server.MinecraftServer.e(MinecraftServer.java:167) at net.minecraft.server.MinecraftServer.c(MinecraftServer.java:154) at net.minecraft.server.MinecraftServer.d(MinecraftServer.java:106) at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:202) at net.minecraft.server.ThreadServerApplication.run(SourceFile:512) Caused by: java.lang.ClassNotFoundException: com.bukkit.narrowtux.DropChest at java.net.URLClassLoader$1.run(URLClassLoader.java:202) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:30) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at java.lang.ClassLoader.loadClass(ClassLoader.java:248) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:247) at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:72)

It says that it cannot load plugins. Note that this is not my terminal but someone
else's that has the same exact problem. I have been searching and found a
few things but I don't understand. I have installed them correctly by dragging
the .jar file into the plugins folder but it still doesn't work. I found this
topic and it fixed it for this person but I don't understand how to on a mac.
Here is the topic http://forums.bukkit.org/threads/invalidpluginexception.3658/#post-711507
Please give me step by step instructions on how to fix this for a MAC not PC
thank you very much

 

Try removing/updating DropChest, this seems to be what is causing the problem

 

sorry like I said that's not my terminal message it's someone elses. I didn't want to start it up to get the message. But I'm having the same problem. This is happening for all my plugins, and there all up-to-date
They said something about changing my plugin.yml but I don't know how to