Problem with RemoteEvents, any help?

I've made a custom chat Gui and after making modifications, it seems to have broken. I have a LocalScript in the PlayerGui that's listening for an OnClientEvent that is being called from a server script, with the argument passed through being a TextLabel with the players chatted message. The label is being created fine on the server but my LocalScript is saying it doesn't exist; it's nil.

Appropriate code inside the server script

local event = Instance.new('RemoteEvent', script) ; event.Name = 'on_chatted'
event:FireAllClients(msg_label)

msg_label is a local variable holding the created TextLabel

Appropriate code inside the local script

event.onClientEvent:connect(function(label)
    shift_labels(label)
end)

The function is regardless for this matter as 'label' apparently doesn't exist.

Am I being stupid? Missing something obvious?

Any help appreciated.

EDIT:

I changed event:FireAllClients(msg_label) by replacing msg_label with an integer, 1.

local event = Instance.new('RemoteEvent', script) ; event.Name = 'on_chatted'
event:FireAllClients(msg_label)

event.onClientEvent:connect(function(x)
    print(x)
end)

The client was able to print the value I sent through, 1. So the problem seems to be with passing a reference to an object. Is this just not doable? If so, is there a workaround?