No worries. Hope you're feeling better.
Thanks for the clarification. The site's looking great! Unfortunately, since Fancybox can only load information present in the source code of a given page, it would be terribly inefficient trying to load several other paginated groups on each view. I'm not really even sure how that could be achieved, to be honest. It might be possible with AJAX pagination, however you'd have to use the Shutter effect for it to work with NextGEN. All I can suggest is to experiment with the number of thumbnails per page at
Gallery --> Options --> Gallery --> "Number of images per page" till you find a sweet spot between the number of pages and images per page.
In regards to the store page, I've just taken a look through your source, and it looks as though you're calling the main image directly/hard-coding it. Is this correct? Optimizer seems to have correctly stripped NextGEN's superfluous scripts, but has not actually added in any of Fancybox's scripts and styles...presumably because you're not using a NextGEN shortcode on the page?
I've just tested your source locally, and have got your current store-bundled Fancybox working by adding an image url to the href attribute in the image's anchor tag. It's currently empty, so Fancybox doesn't have anything to open...hence the message. This is probably the easiest fix, but if you wanted to use Optimizer's Fancybox on the store pages, you should be able to call it just by using NextGEN's [singlepic id=x w=width h=height] shortcode for your store images (unless JigoShop uses it's own post tables).
Hope this helps!