Any idea what this minecraft server message means?

Here is a Warn message I get about every 10 seconds in my minecraft server. Not sure what it is, or what's causing it. It's not affecting anyone it's just annoying and spamming up the console. Thanks in advance.

WARN]: Unexpected character (<) at position 0.
WARN]: at org.json.simple.parser.Yylex.yylex(Unkno… Source)
WARN]: at org.json.simple.parser.JSONParser.nextTo… Source)
WARN]: at org.json.simple.parser.JSONParser.parse(… Source)
WARN]: at org.json.simple.parser.JSONParser.parse(… Source)
WARN]: at org.json.simple.parser.JSONParser.parse(… Source)
WARN]: at com.enjin.officialplugin.threaded.Update…
WARN]: at com.enjin.officialplugin.threaded.Update…
WARN]: at org.bukkit.craftbukkit.v1_7_R1.scheduler…
WARN]: at org.bukkit.craftbukkit.v1_7_R1.scheduler…
WARN]: at java.util.concurrent.ThreadPoolExecutor… Source)
WARN]: at java.util.concurrent.ThreadPoolExecutor$… Source)
WARN]: at java.lang.Thread.run(Unknown Source)

Added (1). Any suggestions? I'm using the 1.7.2 craft bukkit beta build by the way.

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