Bukkit

What steps will reproduce the problem?

What version of are you using?
Bukkit: git-Spigot-044d928-e8c6403 (MC: 1.8.6) (Implementing API version 1.8.6-R0.1-SNAPSHOT)
Vault: v1.5.3-b37
VirtualPack: 2.8.2

Do you have an error log of what happened?
[VirtualPack] Task #1471 for VirtualPack v2.8.2 generated an exception
java.lang.NullPointerException
    at net.drgnome.virtualpack.components.VUncrafterInv$VRecipe.<init>(VUncrafterInv.java:255) ~[?:?]
    at net.drgnome.virtualpack.components.VUncrafterInv$VRecipe.<init>(VUncrafterInv.java:238) ~[?:?]
    at net.drgnome.virtualpack.components.VUncrafterInv.init(VUncrafterInv.java:68) ~[?:?]
    at net.drgnome.virtualpack.VPlugin$1.run(VPlugin.java:175) ~[?:?]
    at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftTask.run(CraftTask.java:71) ~[spigot.jar:git-Spigot-044d928-e8c6403]
    at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:350) [spigot.jar:git-Spigot-044d928-e8c6403]
    at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:726) [spigot.jar:git-Spigot-044d928-e8c6403]
    at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:367) [spigot.jar:git-Spigot-044d928-e8c6403]
    at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:657) [spigot.jar:git-Spigot-044d928-e8c6403]
    at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:560) [spigot.jar:git-Spigot-044d928-e8c6403]
    at java.lang.Thread.run(Thread.java:745) [?:1.8.0_25]

Please provide any additional information below.

on enable display this error

Uh... I can fix this, but it looks more like your Minecraft server is broken.
Are you using any plugins that add custom crafting recipes?

Fixed in dev build #150 (1.8.8 compatible). Are you able to switch to 1.8.8, or able to compile VirtualPack yourself?