Bukkit

What steps will reproduce the problem?
1. Install plugin
2. Start server
3.

What is the expected output? What do you see instead?
I expect the command to work, end up with a "unknown command" error instead.

What version of the product are you using?
Ioncannon_V1.5.jar

Do you have an error log of what happened?

From the server's console:
10:31:38
CONSOLE:
[SEVERE] Could not load 'plugins/Ioncannon_V1.5.jar' in folder 'plugins'
10:31:38
CONSOLE:
nl/xesxen/Ioncannon/IonCannon : Unsupported major.minor version 51.0
10:31:38
CONSOLE:
java.lang.UnsupportedClassVersionError: nl/xesxen/Ioncannon/IonCannon : Unsupported major.minor version 51.0

Please provide any additional information below.