Bukkit

What steps will reproduce the problem?
1.Restart the server
2.every 10 minutes it will throw error to the console.
3.

What is the expected output? What do you see instead?
I assume nothing or a message about saving showcases, I get the output pasted in the link below.

What version of the product are you using?
latest dev build

Do you have an error log of what happened?
http://pastie.org/3588641

Please provide any additional information below.
the plugin works fine players can build and use all showcases fine. the error is just shown in the console but nothing seems affected.