I have the same issue with the page showing up blank.

I have version 1.3.8a. I have IH2 & Zen lightbox.

I ran some tests tonight and I found that if I have one product (item) it will show a blank page. However, if I have two products the page appears to be normal.

Conclusion: One item will produce a blank page.

Two items appears to be normal and both items will show up.