bridge script failing when added as menu item

The following script will not run in when wrapped in a menu item. But the main function runs fine on its own...

Any idea whats going on. 

#target bridge

var menu = MenuElement.create( "command", "Anon_forSending", "at the end of Tools");

menu.onSelect = function(m) { main() }


function main(){ 
    var selectedThumbnails = app.documents[0].getSelection();
        var modified = 0;
        for (var i = 0; i < selectedThumbnails.length; ++i) {
                            var val = decodeURI(selectedThumbnails[i].name);
                            var f = new File (decodeURI(selectedThumbnails[i].path))
            if (stripFileExtension)
                val = val.replace(/\.[^\.]+$/, '');
    p = (val.match(/_0/).index)+1
    val =val.substr(p,4)
    newName = val + '.psd'
    var f1 = new File (f.parent + "/" + newName)
    if (f1.exists == true){newName = val + '_1' + '.psd'}
    
            var metadata = selectedThumbnails[i].synchronousMetadata;
              metadata.namespace = 'http://ns.adobe.com/photoshop/1.0/';
            metadata.applyMetadataTemplate("clearall", "replace")
            selectedThumbnails[i].name = newName
 
        }

            }