MapPageRoute routeUrl hitting 403 on specific request

I currently using global.asax for my page routing on my website.

Except I have the following code:

//Home:
routes.MapPageRoute("intro", String.Empty, "~/Default.aspx");
routes.MapPageRoute("home", "home", "~/Default.aspx");

//EHBO:
routes.MapPageRoute("ehbo-overzicht", "ehbo/overzicht",  "~/ehbo/overview.aspx");
routes.MapPageRoute("ehbo-input", "ehbo/input", "~/ehbo/input.aspx");
routes.MapPageRoute("ehbo-input-edit", "ehbo/inputedit/{itemid}", "~/ehbo/inputedit.aspx");

//Links:
routes.MapPageRoute("links", "links/links", "~/links/overview.aspx");

However for Links I want to use :

//Links:
routes.MapPageRoute("links", "links", "~/links/overview.aspx");

But this isn't working for me. I'm getting the following error: HTTP-fout 403.14 - Forbidden

I am using authentication on my map ehbo, but nothing else, web.config:

<!-- Authentication -->
<authentication mode="Forms">
    <forms loginUrl="~/Login" name=".ASPXFORMSAUTH" defaultUrl="home">
    </forms>
</authentication>
<authorization>
    <allow users="*"/>
    <deny users="?" />
</authorization>

<location path="ehbo">
    <system.web>
        <authorization>
            <deny users="?"/>
        </authorization>
    </system.web>
</location>

But I don't think this is the problem. Because if I don't use authentication I'm getting the same error.

Someone that knows the answer?