I have a very simple gallery to create on page. Here are the bits I have put together for this task. 

First I created a new media folder and in it put a few files. Each files is a jpg image. 

For now each is called GalleryImage but I don't think that is the issue here. 

I next created a Razor marco. Umbraco gave me a head start on this and for now i have left the razor code as Umbraco supplied bar some test values.  Here it is. 

@inherits umbraco.MacroEngines.DynamicNodeContext

@*
Macro Parameters To Create, for this macro to work:
Show:True   Alias:mediaId     Name:Media Folder ID    Type:MediaCurrent
*@


@if (Parameter.mediaId != null)
{
     @* Get the media folder as a dynamic node *@
    var mediaFolder =  Library.MediaById(Parameter.mediaId);

    if (mediaFolder.Children.Any())
    {
        <ul>
            @* for each item in children of the selected media folder *@
            @foreach (var mediaItem in mediaFolder.Children)
            {
                <li><img src="@mediaItem.umbracoFile" alt="@mediaItem.Name" /></li>
            }
        </ul>
    }else
    {
            <ul>
                <li>test</li>
            </ul>
    }

    <h3>here</h3>
}

Finally, I placed the macro in the template.  

<umbraco:Macro Alias="Gallery" runat="server" mediaId="1117" />

. . . where 1117 is the id of the GalleryImages folder above. 

When run the page NOTHING appears. No error, not markup, no images, nothing. It's like the macro is getting ignored. You can see why I added the else condition, and then in despiration I added the h3 title. 

What am I missing here?