by looking at the log, I can see that you have an error with the onPacketReceiving(PacketEvent) for ItemsAdder java.lang.IllegalAccessError: class ia.m.hJ tried to access the method void org.bukkit.event.player.PlayerEvent.<init>(org.bukkit.entity.Player, boolean)
I can't provide and extra reason for what happens without the full log, but if this is the first installation, make sure to follow the wiki for instructions
also, if you added costume configurations make sure to check if you did everything right
please provide the full, it will give us a better picture on what's hapnning
