Why does my minecraft server keep crashing?

Why does my minecraft server keep crashing?
Added (1). Why does my minecraft server keep crashing? It says this

---- Minecraft Crash Report ----
// Oh - I know what I did wrong!

Time: 5/17/15 9:13 PM
Description: Watching Server
Added (2). there is only 2 people on it and no mods just started it today and have barely done anything yet

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