[Foxlit]

Originally Posted by Slakah "FRAME" should be "Frame"

That makes no difference whatsoever.

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Your indentation is a bit weird, and the last else clause would never run (but everything should work without changes). It can be cleaned up and shortened a bit:

local f = CreateFrame("FRAME", "Frame_fStealth");
f:RegisterEvent("UPDATE_STEALTH");

local function eventHandler(self, event, ...)
	local nStance = GetShapeshiftForm();
	EquipmentManager_EquipSet(nStance == 0 and "Normal" or "Stealth");
end
f:SetScript("OnEvent", eventHandler);