I downloaded the minecraft_server.jar. I tried to install Industrial craft and modloadermp. After trying about 10 times all with fresh .jar files it doesnt work. The wierd thing is that when i try to open the file it says i dont have permission to open it and its corrupted.
6/7/11 7:06:05 PM [0x0-0xd80d8].com.apple.JarLauncher[1144] Invalid or corrupt jarfile /Users/Desktop/server/minecraft_server.jar
Try not playing with mods and see what happens. If you're not getting access to files, make sure you're the one with all the permissions to open them such as running as administrator and confirming you're using the master account.
6/7/11 7:06:05 PM [0x0-0xd80d8].com.apple.JarLauncher[1144] Invalid or corrupt jarfile /Users/Desktop/server/minecraft_server.jar