i have the folloning macro iam tryning to get to runn..

i keep getting this error.. https://i.imgur.com/FMyVpu0.png

it is an old macro i made for v7.

and to be onest im that good at the varsion 8 way off doning it yet..

might som be able to help me fix it

@inherits Umbraco.Web.Macros.PartialViewMacroPage
@using Umbraco.Web


@*
    Macro to list all child pages under a specific page in the content tree.

    How it works:
        - Confirm the startNodeId macro parameter has been passed in with a value
        - Loop through all child pages
        - Display a list of link to those pages, sorted by the value of the propertyAlias

    Macro Parameters To Create, for this macro to work:
    Alias:startNodeId     Name:Select starting page    Type:Content Picker
*@

@{ var startNodeId = Model.MacroParameters["startNodeId"]; }

@if (startNodeId != null)
{
    @* Get the starting page *@
    var startNode = Umbraco.Content(startNodeId);
    var selection = startNode.Children.Where(x => x.IsVisible()).ToArray();

    if (selection.Length > 0)
    {   
        <ul>
            @foreach (var item in selection)
            {
                <li>

                                <!-- LAYER Headline -->
                                <div class="tp-caption SliderTekstHeadline sfr tp-resizeme"
                                    data-x="0"
                                    data-y="70" 
                                    data-speed="600"
                                    data-start="1200"
                                    data-end="9400"
                                    data-endspeed="600">@Model.Value("slideHeadline")
                                </div>

                                <!-- LAYER Textline 1 -->
                                <div class="tp-caption sfb SliderTekst tp-resizeme"
                                    data-x="0"
                                    data-y="140" 
                                    data-speed="600"
                                    data-start="1600"
                                    data-end="9400"
                                    data-endspeed="600">@Model.Value("slideTekst1")
                                </div>


                                <!-- LAYER Textline 2 -->
                                <div class="tp-caption sfb SliderTekst tp-resizeme"
                                    data-x="0"
                                    data-y="190" 
                                    data-speed="600"
                                    data-start="2000"
                                    data-end="9400"
                                    data-endspeed="600">@Model.Value("slideTekst2")
                                </div>


                                <!-- LAYER Textline 3 -->
                                <div class="tp-caption SliderTekst sfb tp-resizeme"
                                    data-x="0"
                                    data-y="240" 
                                    data-speed="600"
                                    data-start="2400"
                                    data-end="9400"
                                    data-endspeed="600">@Model.Value("slideTekst3")
                                </div>

                                <!-- LAYER Textline 4 -->
                                <div class="tp-caption sfb SliderTekst tp-resizeme"
                                    data-x="0"
                                    data-y="290" 
                                    data-speed="600"
                                    data-start="3200"
                                    data-end="9400"
                                    data-endspeed="600">@Model.Value("slideTekst4")
                                </div>


                                <!-- LAYER Textline 5 -->
                                <div class="tp-caption sfb SliderTekst tp-resizeme"
                                    data-x="0"
                                    data-y="340" 
                                    data-speed="600"
                                    data-start="3600"
                                    data-end="9400"
                                    data-endspeed="600">@Model.Value("slideTekst5")
                                </div>


                                <!-- LAYER Textline 6 -->
                                <div class="tp-caption SliderTekst sfb tp-resizeme"
                                    data-x="0"
                                    data-y="390" 
                                    data-speed="600"
                                    data-start="4000"
                                    data-end="9400"
                                    data-endspeed="600">@Model.Value("slideTekst6")
                                </div>

                                <!-- LAYER Image -->
                                <div class="tp-caption sfr tp-resizeme SliderImage"
                                    data-x="570"
                                    data-y="center" 
                                    data-speed="600"
                                    data-start="2200"
                                    data-end="9400"
                                    data-endspeed="600">
                                    <img src="@Model.Value("image")" class="SliderRadius" />
                                </div>

                                </li>
            }
        </ul>
    }
}