WoWInterface - Error with runes

I'm getting this error any time my screen reloads:

Code:

36x BasicUI\Modules\Powerbar.lua:316: attempt to perform arithmetic on local 'start' (a nil value)

[string "@BasicUI\Modules\Powerbar.lua"]:316: in function <BasicUI\Modules\Powerbar.lua:314>

[string "@BasicUI\Modules\Powerbar.lua"]:495: in function <BasicUI\Modules\Powerbar.lua:480>



Locals:

self = 1

start = nil

duration = nil

runeReady = nil

(*temporary) = <function> defined =[C]:-1

(*temporary) = 173940.047000

(*temporary) = 173940.047000

(*temporary) = nil

(*temporary) = "attempt to perform arithmetic on local 'start' (a nil value)"

floor = <function> defined =[C]:-1

this is the code block that is coming from:

Code:

        local function CalcRuneCooldown(self)

                local start, duration, runeReady = GetRuneCooldown(self)

                local time = floor(GetTime() - start)

                local cooldown = ceil(duration - time)



                if (runeReady or UnitIsDeadOrGhost('player')) then

                        return '#'

                elseif (not UnitIsDeadOrGhost('player') and cooldown) then

                        return cooldown

                end

        end

The bold part of the code is line 316 where the error is coming from any suggestions?
Thanks
Coke