Bukkit

What is the issue?
Me and my friends have downloaded this plugin and it was working really well until now where ive sat on a seat and it glitched and now i cant get back on the server, when i do try and get back on, it says 'Nope' and we've tried everything to fix it: Restarting the server, taking out the jar file and the folder out of my files for the server.. We cannot delete this world because it is too precious
Please provide any additional information below.

Ask your friend or the server owner to remove you from he server files like your player data this will set you back to the spawn point and you may lose your files :(