Tony,
I was doing some research on nutrient deficiencies in bananas in that site I just posted this afternoon (Pest and Disease of Bananas) and I was reading about Boron and Calcium deficiency. I remembered this post of yours. Boron deficiency looks like it could be the problem to me. Check out the site when you get a chance. Here is the link to a Power Point presentation found on that site.
http://www.ctahr.hawaii.edu/nelsons/...management.pdf
For the link to the entire site see my post from earlier today. Hope this helps you.
Seems like others have posted with photos of banana leaves with only a midrib and no leaf blade. That appears to be caused by Calcium deficiency (unless you actually see grasshoppers or caterpillars!). Everyone should really check out this web site as it has a lot of great info.