Unable to cast Instance to bool,what?

Why does it say this is it because of line 13 and it's loop?If so why and how do I fix it? Output:

22:51:16.693 - Unable to cast Instance to bool 22:51:16.694 - Script 'Workspace.Script', Line 12 - global MakeDisplayArms 22:51:16.694 - Script 'Workspace.Script', Line 28 22:51:16.695 - Stack End 22:51:16.695 - Disconnected event because of exception

game.Players.PlayerAdded:connect(function(Player)
		Player.CharacterAdded:connect(function(Character)
---------------------------------------------------------
			function MakeDisplayArms()
---------------------------------------------------------
				local CurrentCamera = game.Workspace.CurrentCamera
				local PlayerArms = {
					Character["Right Arm"],
					Character["Left Arm"]}
---------------------------------------------------------
					for i,v in pairs (PlayerArms) do
FoundClonedArms = CurrentCamera:FindFirstChild("Cloned",v)--Finds for Cloned parts
				if not FoundClonedArms then--Litte debounce
						local ClonedArms = v:Clone()
						ClonedArms.Parent = CurrentCamera--Hides it from everyone else
						ClonedArms.Name = "Cloned",v--Renames it
						ClonedArms.CanCollide = false
						local Weld = Instance.new("Weld")
							Weld.Part0 = v--Welds it Arms
							Weld.Part1 = ClonedArms
						return ClonedArms
						else
					return FoundClonedArms
					end
				end
			end
---------------------------------------------------------			
			MakeDisplayArms()
		end)
end)

What is this script suppose to do? This script is suppose to make a fake arm that is hidden in the CurrentCamera and that the player can see his arm when zoomed in.

The problem is EXACTLY what it says it is. The second argument to findFirstChild() is a BOOL value, v is an INSTANCE.

The CORRECT way to add strings together is by using ".."

Example

local MyString = "Hello "
local player = "Player"

local JoinedString = MyString .. player

print(JoinedString)
--> Hello Player

Your code would be

game.Players.PlayerAdded:connect(function(Player)
        Player.CharacterAdded:connect(function(Character)
---------------------------------------------------------
            function MakeDisplayArms()
---------------------------------------------------------
                local CurrentCamera = game.Workspace.CurrentCamera
                local PlayerArms = {
                    Character["Right Arm"],
                    Character["Left Arm"]}
---------------------------------------------------------
                    for i,v in pairs (PlayerArms) do -- IS V A OBJECT OR A STRING? IF IT IS AN OBJECT, I WOULD USE v.Name
FoundClonedArms = CurrentCamera:FindFirstChild("Cloned_" .. v)--Finds for Cloned parts
                if not FoundClonedArms then--Litte debounce
                        local ClonedArms = v:Clone()
                        ClonedArms.Parent = CurrentCamera--Hides it from everyone else
                        ClonedArms.Name = "Cloned_" .. v--Renames it
                        ClonedArms.CanCollide = false
                        local Weld = Instance.new("Weld")
                            Weld.Part0 = v--Welds it Arms
                            Weld.Part1 = ClonedArms
                        return ClonedArms
                        else
                    return FoundClonedArms
                    end
                end
            end
---------------------------------------------------------           
            MakeDisplayArms()
        end)
end)

Disclaimer: untested code, report future problems.

I see you're trying to concatenate a string, try this.

game.Players.PlayerAdded:connect(function(Player)
        Player.CharacterAdded:connect(function(Character)
---------------------------------------------------------
            function MakeDisplayArms()
---------------------------------------------------------
                local CurrentCamera = game.Workspace.CurrentCamera
                local PlayerArms = {
                    Character["Right Arm"],
                    Character["Left Arm"]}
---------------------------------------------------------
                    for i,v in pairs (PlayerArms) do
FoundClonedArms = CurrentCamera:FindFirstChild("Cloned_"..v.Name)--Finds for Cloned parts
                if not FoundClonedArms then--Litte debounce
                        local ClonedArms = v:Clone()
                        ClonedArms.Parent = CurrentCamera--Hides it from everyone else
                        ClonedArms.Name = "Cloned_"..v.Name --Renames it
                        ClonedArms.CanCollide = false
                        local Weld = Instance.new("Weld")
                            Weld.Part0 = v--Welds it Arms
                            Weld.Part1 = ClonedArms
                        return ClonedArms
                        else
                    return FoundClonedArms
                    end
                end
            end
---------------------------------------------------------           
            MakeDisplayArms()
        end)
end)

More information: http://wiki.roblox.com/index.php?title=Concatenation