Your index page has several HTML errors which should be fixed.
Your document should use a Doctype Declaration, it has 2 </head> tags and the opening <html> tag is half way down the page.
Also, your 'gallery.xml' file has a parsing error.
The opening and closing tags should match (you have <GALLERY_DATA> and </gallery>).
Change the opening tag to:
<gallery cellDimension="750" columns="6" zoomOutPerc="15" zoomInPerc="100" frameWidth="20" frameColor="0xFFFFFF" captionColor="0xFFFFFF" enableRightClickOpen="true">
These suggestions may not fix the problem (it may be the speed of your web server) but it would be wise to iron out any and all errors found.
SimpleViewer Support Team