Problem with Viewer.open method

I hold a tilesource collection in a variable:

 var docFile = new Array (
                "/render/588a9ee5-6ae4-4500-8c99-17877b78e632/1.dzi",
                "/render/588a9ee5-6ae4-4500-8c99-17877b78e632/2.dzi",
                "/render/588a9ee5-6ae4-4500-8c99-17877b78e632/3.dzi",
                "/render/588a9ee5-6ae4-4500-8c99-17877b78e632/4.dzi",
                "/render/588a9ee5-6ae4-4500-8c99-17877b78e632/5.dzi",
                "/render/588a9ee5-6ae4-4500-8c99-17877b78e632/6.dzi",
                "/render/588a9ee5-6ae4-4500-8c99-17877b78e632/7.dzi",
                "/render/588a9ee5-6ae4-4500-8c99-17877b78e632/8.dzi",
                "/render/588a9ee5-6ae4-4500-8c99-17877b78e632/9.dzi"
            );

If I  initialize the Viewer it works, if I use the open-method later I get an error in:

resetContentSize: function( contentSize ){
        this.contentSize    = contentSize;
 -->       this.contentAspectX = this.contentSize.x / this.contentSize.y;

work:
var Viewer = OpenSeadragon({
                id: "Viewer",
                immediateRender: true,
                navigatorSizeRatio: 0.25,
                prefixUrl: "openseadragon/images/",
                wrapHorizontal: false,
                tileSources: docFile                
            });

doesn't work:
 Viewer.open(docFile);

What do I make wrong?