quest error

[14:48:12] [Craft Scheduler Thread - 24/WARN]: Couldn't look up profile properties for net.minecraft.util.com.mojang.authlib.GameProfile@1ad841d3[id=881cb2ca-7437-4150-846b-6f1bc0dc5ad4,name=,properties={},legacy=false]
net.minecraft.util.com.mojang.authlib.exceptions.AuthenticationException: The client has sent too many requests within a certain amount of time
at net.minecraft.util.com.mojang.authlib.yggdrasil.YggdrasilAuthenticationService.makeRequest(YggdrasilAuthenticationService.java:65) ~[spigot.jar:git-Spigot-1494]
at net.minecraft.util.com.mojang.authlib.yggdrasil.YggdrasilMinecraftSessionService.fillProfileProperties(YggdrasilMinecraftSessionService.java:135) [spigot.jar:git-Spigot-1494]
at net.citizensnpcs.npc.entity.HumanController$SkinFetcher.run(HumanController.java:117) [Citizens.jar:?]
at org.bukkit.craftbukkit.v1_7_R3.scheduler.CraftTask.run(CraftTask.java:67) [spigot.jar:git-Spigot-1494]
at org.bukkit.craftbukkit.v1_7_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53) [spigot.jar:git-Spigot-1494]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [?:1.7.0_40]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [?:1.7.0_40]
at java.lang.Thread.run(Thread.java:724) [?:1.7.0_40]