Problem/Bug How can i fix that?

1. 1. org.bukkit.configuration.serialization.ConfigurationSerialization] Could not call method 'public static org.bukkit.inventory.ItemStack org.bukkit.inventory.ItemStack.deserialize(java.util.Map)' of class org.bukkit.inventory.ItemStack for deserialization
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      [11:35:04 WARN]: [QuickShop] You can try force load this ItemStack by our hacked ItemStack read util(shop.force-load-downgrade-items), but beware, the data may corrupt if you load on this lower Minecraft server version, Please backup your world and database before enable!

and than come that error:

1. 1. [11:35:04 ERROR]: [org.bukkit.configuration.serialization.ConfigurationSerialization] Could not call method 'public static org.bukkit.inventory.ItemStack org.bukkit.inventory.ItemStack.deserialize(java.util.Map)' of class org.bukkit.inventory.ItemStack for deserialization

i need help