Why am I getting the gui error?

my code:

local serverStorage = game:GetService("ReplicatedStorage")
local sc = script.Parent
local inT = sc
local outT = sc.Parent.Output
local I = serverStorage.InfoScreens
local player = game.Players.LocalPlayer
local loadOver = false
local OutputText
local playerGUI = sc.Parent.Parent.Parent
local Console1 = playerGUI.Console1
local Console3 = playerGUI:WaitForChild("Console3")
local ErrorTxt
local OUTTXT = "Output"

local function clearIn()
	inT.Text = ""
end
local function clearOut()
	outT.Text = ""
end

local function start()
	Console1.Console.Frame.Visible = true
	Console1.Console.Input.Visible = true
	Console1.Console.Output.Visible = true
	
	Console3.Console.Frame.Visible = true
	Console3.Console.Input.Visible = true
	Console3.Console.Output.Visible = true
end

local function checkForInputStart()
	if sc:IsFocused() == false then
		if inT.Text == "start" then
			outT.Text = "start \n Start!"
			start()
			clearIn()
			print("start")
			loadOver = true
			return
		elseif inT.Text == "help" then		
			
			outT.Text = "help \n Help with what?"
			clearIn()
		elseif inT.Text == "about" then
			
			outT.Text = "About what?"
			clearIn()
		elseif inT.Text == "" then
			--nothing
		else
			ErrorTxt = inT.Text
			OUTTXT = ErrorTxt, "\n Error ", ErrorTxt "does not exist in the command database"
			clearIn()
		end
	end
end

local function checkForInput()
	
	
	
end

while true do 
	if loadOver == false then
	checkForInputStart()
	else
		checkForInput()
	end
	outT.Text = OUTTXT
	wait(0.1)
end

my error 19:48:00.018 - Players.Player1.PlayerGui.Console2.Console.Input. LocalScript:53: attempt to call upvalue 'ErrorTxt' (a string value)

can anyone tell em what I'm doing wrong?