WORLDEDIT-2376 - Reported by Vitama

When I try to do //set or //walls....i get an error:

java.lang.NoClassDefFoundError: net/minecraft/server/Block

The version of WorldEdit is 5.4.5, bukkit (craftbukkit-1.4.5-R0.3-20121206.015911-26).
I have essentials too, anything more