"partOrCharcter must be in workspace". What does that mean?

So I made a quest giver, and when you complete the quest the dialog that's supposed to appear doesn't and the output says partOrCharacter must be in the workspace. I am very confused by this

if plr.MainTask.Value == "QuestComplete" then

wait(1)

workspace:WaitForChild("NPC"):Destroy()

game.ReplicatedStorage.Folder.SubFolder2.NPC:Clone().Parent = workspace

end

I destroy and clone a the NPC that has a different dialog so that it makes a makes a new dialog appear, but when you walk up to it, the dialog disappears with this in the output:

16:39:55.108 - partOrCharacter must be in the Workspace

16:39:55.109 - Stack Begin

16:39:55.112 - Script 'CoreGui.RobloxGui.CoreScripts/MainBotChatScript2', Line 314 - upvalue chatFunc

16:39:55.112 - Script 'CoreGui.RobloxGui.CoreScripts/MainBotChatScript2', Line 515 - global doDialog

16:39:55.113 - Script 'CoreGui.RobloxGui.CoreScripts/MainBotChatScript2', Line 567 - global startDialog

16:39:55.113 - Script 'CoreGui.RobloxGui.CoreScripts/MainBotChatScript2', Line 717

16:39:55.113 - Stack End