STOP THE SERVER.
Then,
Delete all the other jars in your root directory
Go back to the main page,
select CraftBukkit.jar
Click "Save"
Click start.
Does it crash?
Another thing to think about is if you download plugins via BukGet Plugins on multicraft, it takes up twice the space. So, you need to remove all of those by,
click on Bukget Plugins,
Click on currently installed,
If any of those you previously deleted the jar for, click on it,
Click remove.
