bad argument

[kawe]

Message: Interface\AddOns\oUF_Mu\core\layout.lua:242: bad argument #2 to 
'SetFormattedText' (string expected, got boolean)
Time: 09/25/15 21:04:13
Count: 1
Stack: [C]: in function `SetFormattedText'
Interface\AddOns\oUF_Mu\core\layout.lua:242: in function
 <Interface\AddOns\oUF_Mu\core\layout.lua:241>
(tail call): ?
(tail call): ?
(tail call): ?
Interface\AddOns\oUF\elements\altpowerbar.lua:143: in function `func'
Interface\AddOns\oUF\events.lua:48: in function <Interface\AddOns\oUF\events.lua:46>
(tail call): ?

Locals: (*temporary) = <unnamed> {
 0 = <userdata>
}
(*temporary) = "%s: %i"
(*temporary) = false
(*temporary) = 25
(*temporary) = "string expected, got boolean"

can anyone please explain whats wrong with the formatting and how to fix it?

shouldve pasted the actual code from the core file

if cfg.altpowerbar then		-- alt power bar skinning
			local altpower = CreateFrame('StatusBar', nil, UIParent)
			altpower:SetStatusBarTexture(cfg.powertex)
			altpower:SetStatusBarTexture(0.6, 0.6, 0.6)
			altpower:SetSize(160, 4)
			altpower:SetPoint('TOP', 0, -136)
			
			local bg = altpower:CreateTexture(nil, 'BACKGROUND')
			bg:SetAllPoints(altpower)
			bg:SetTexture(0.1, 0.1, 0.1, 0.75)
			altpower.bg = bg
			
			local value = altpower:CreateFontString(nil, 'OVERLAY')
			value:SetFont(cfg.font, cfg.fontsize, cfg.fontflag)
			value:SetPoint('TOP', altpower, 'BOTTOM', 0, -4)
			altpower.value = value
			
			altpower.border = mu.createBorder(altpower)
			altpower.PostUpdate = function(Bar, min, cur, max)
			Bar.value:SetFormattedText('%s%s', Bar.powerName, cur)
			end
			
			self.AltPowerBar = altpower
		end