Bukkit

What steps will reproduce the problem?
1. I think it's when you use /land claim but I only happens occasionally.

What is the expected output? What do you see instead?
It seem to still claim the area but it throws an error.

What version of the product are you using?
Latest v1.3.

Do you have an error log of what happened?
Yes: http://pastebin.com/LLdXtbMn

Please provide any additional information below.
I'm using Spigot 1.8.3.

I just checked the code and I realized that I've used both EssentialsProtect and WorldGuard. I removed EssentialsProtect and hopefully the error is gone, I'll keep you updated.

@BaconFred: Go

Ok do let me know if that was the cause of the problem.

@Jcdesimp: Go

I think it was, however, are you planning on adding protection for mounting horses?

@BaconFred: Go

I decided against adding that because there is no way of determining who the rightful owner of a horse is. For example if someone rides a horse into someone else land and dismounts there, their horse will be stuck there.

The solution to protecting your horses is simply to keep them safe inside, the animal protection and anti-build flags should keep it safe in that scenario.