VBScript中的字典类型不匹配

样式表定义为:

sub stylesheets(collection)
    for each key in collection.Keys
        response.write(stylesheet(key, collection.Item(key)))
    next
end sub

' returns a link tag for each object in the collection
function stylesheet(asset, media_type)
    if (media_type="") then
        media_type="screen"
    end if
    return "<link href=""" & asset_url(asset) & """ type=""text/css"" media=""" _
        &  media_type & """ />"
end function

<% stylesheets(site_stylesheets) %>

其中site_样式表定义为:

' stylesheets is a collection of the stylesheets to be included on all pages
Set site_stylesheets = CreateObject("Scripting.Dictionary")
site_stylesheets.Add "css/endoworks.css", "screen"

我已经很久没有做任何VBScript了。我真的很感激任何帮助。