Script on custom attribut controller problem

Hi, Before to start with my problem, thanks for your website, really usefull ! I'm working on a simple script to batch a controller with several options, it work perfectly on a classic controller like a position but not on a custom attribut and i can't find my error. Please find bellow a short version of my script ( this part bake controller )

<code>

fn bakeMe ctrl fromRange:animationRange.start toRange:animationRange.end = (
    fromRange = fromRange as time
    toRange = toRange as time

    if (superclassof ctrl.controller) != FloatController do -- ctrl doit-être un controler de type float
        (
            print "Only work on FloatController superClass"
            return false
        )

    undo "BakeControler " on (
        tmpVal=#()
        try (
            -- record value
                for i = fromRange to toRange do (
                    at time i (
                        append tmpVal ctrl.controller.value
                    )
                )
            -- assign new controller
                ctrl.controller=linear_float()

            --applying value to the new controller
                for i = fromRange to toRange do (
                    at time i (
                        numID =((i.frame)+1-(fromRange.frame as integer)) as integer
                        with animate on (
                            ctrl.controller.value = tmpVal[numID]
                        )
                    )
                )

        )catch(
            format "*** BakingError: % ***\n" (getCurrentException())
        )
    )
)

bakeMe $.position.controller[1] -- Work perfeclty

bakeMe bakeMe $.baseObject.Custom_Attributes.param1 -- Crash with Unknown property: "controller" in 6.69115 ( value )

</code>

Thanks for your help