Bukkit

What steps will reproduce the problem?
1.When im about to disguise it says: error occured
2.I cannot disguise
3.It still kinda works just that i cannot disguise

What is the expected output? What do you see instead?

When im about to disguise it says: error occured

What version of the product are you using?
1.2.4 (But mob disguise still works above i seen it before)

Do you have an error log of what happened?
Yes

Please provide any additional information below.
It wont let me disguise as a mob