To understand how this particular site works, you might want to click the question mark tab in the toolbar at the bottom of the page. Using the appropriate tool you may print individual pages of a publication, or download them in their entirety. However, you may need a subscription to view or download material from different publications accessible via this site.
While you cannot print the entire 'page'* to PDF in the regular way you tried, you can do so with individual articles. The site has a built-in Reader function (as in Safari 5), and clicking on eligible items at the low-mag view will bring up a Reader window with a grey window bar at the top and a close button (X) at the top right. These windows can be printed to PDF.
*) The page is in fact an overview of a multiple page publication, with a larger window-fitting version of the page selected in the center, and the other pages represented as thumbnails in the column on the right. If you print to PDF at this view, you're going to get that empty page. Things get different when you click on that low-mag page in the center of the page. You either get an enlargement of it, or a new Reader-like window. Both can in fact print to PDF, but depending on the effect of your click you may get a bunch of thumbnails, a representation of that selected central page, or a magnified portion of it.
