SetCore: X has not been registered by the CoreScripts

What the message means

Players.Builderman.PlayerScripts.DisableReset:4: SetCore: ResetButtonCallback has not been registered by the CoreScripts

Other forms of the same message:

• SetCore: SendNotification has not been registered by the CoreScripts
• SetCore: ChatMakeSystemMessage has not been registered by the CoreScripts
• GetCore: ChatActive has not been registered by the CoreScripts

The CoreScripts load alongside your own scripts when a player joins. A LocalScript in StarterPlayerScripts or StarterGui can run before they finish, and Roblox's own reference for SetCore says to call it several times with pcall for that reason.

SetCore only works on the client. From a server Script the message is different: StarterGui:SetCore must be called from a local script.

Causes and fixes

Three things cause this error in practice. Each one below has the smallest code that triggers it, then the fix.

• SetCore runs before the CoreScripts are ready
• The name is misspelt or does not exist
• ChatMakeSystemMessage in a game on TextChatService

SetCore runs before the CoreScripts are ready

Turning off the reset button in the first line of a LocalScript is the textbook case: it works on a fast computer and fails on a slow one, or only sometimes.

local StarterGui = game:GetService("StarterGui")

-- runs at once: SetCore: ResetButtonCallback has not been registered by the CoreScripts
StarterGui:SetCore("ResetButtonCallback", false)

Call it in a pcall and try again after a short wait until it works. Give up after a number of tries so a name that never registers does not loop for ever.

local StarterGui = game:GetService("StarterGui")

local function setCoreWhenReady(name: string, value: any, tries: number?)
	for _ = 1, tries or 50 do
		local ok = pcall(StarterGui.SetCore, StarterGui, name, value)
		if ok then
			return true
		end
		task.wait(0.2)
	end
	warn(`[SetCore] {name} never registered`)
	return false
end

setCoreWhenReady("ResetButtonCallback", false)

The name is misspelt or does not exist

The first argument is a plain string, so the Script Editor cannot check it. TopBarEnabled, ResetButtonCallBack or SendNotifcation are never registered, so they fail every time, and no amount of waiting helps.

local StarterGui = game:GetService("StarterGui")

-- the name is TopbarEnabled (lower-case b)
StarterGui:SetCore("TopBarEnabled", false)

Copy the exact name from the StarterGui:SetCore reference. If a retry loop like the one above never succeeds, check the spelling before anything else.

local StarterGui = game:GetService("StarterGui")

for _ = 1, 50 do
	if pcall(StarterGui.SetCore, StarterGui, "TopbarEnabled", false) then
		break
	end
	task.wait(0.2)
end

ChatMakeSystemMessage in a game on TextChatService

ChatMakeSystemMessage belongs to the legacy chat system. Roblox's reference says it needs TextChatService.ChatVersion set to LegacyChatService, which is deprecated. In a game using the current TextChatService, the name is never registered.

local StarterGui = game:GetService("StarterGui")

-- legacy chat only: SetCore: ChatMakeSystemMessage has not been registered by the CoreScripts
StarterGui:SetCore("ChatMakeSystemMessage", {
	Text = "Round starting!",
	Color = Color3.fromRGB(255, 200, 0),
})

Use TextChannel:DisplaySystemMessage on the general channel instead. It runs on the client and shows the message to that player only.

local TextChatService = game:GetService("TextChatService")

local channels = TextChatService:WaitForChild("TextChannels")
local general = channels:WaitForChild("RBXGeneral") :: TextChannel

general:DisplaySystemMessage("Round starting!")

How to find the line that causes it

1. Open Output (Window menu, or the Script tab), clear it with Ctrl+K (⌘K on Mac), and press Play.
2. Find the first red line. It starts with the script's place in the Explorer and the line number, such as ServerScriptService.Shop:12:.
3. Click the red line. Studio opens that script with the cursor on the failing line.
4. Read the lines between Stack Begin and Stack End under it: they list the calls that led there, newest first, so you can see which function called the broken one.
5. Still not sure which value is wrong? Add print(typeof(x), x) just above the line, or set a breakpoint on it and read the values in the Watch window.

Questions

Sources and further reading

• Roblox Creator Docs: StarterGui:SetCore. the accepted names, and calling it with pcall until the core script has loaded
• Roblox Creator Docs: TextChannel:DisplaySystemMessage
• Roblox Creator Docs: TextChatService

How the code was checked: every block marked Fixed passes Luau's strict type checker against Roblox's API definitions (luau-lsp, 4 November 2026), and every block marked Breaks compiles and fails only when it runs. The message wording, including the GetCore form, was checked against the message format strings in Roblox Studio itself (macOS build installed on 24 October 2026) on 4 November 2026. The SetCore names and the advice to retry with pcall are from the StarterGui:SetCore reference in the Roblox creator docs. A type check catches misspelt APIs and wrong types, not game logic, so playtest in Studio before you publish.