Ah! I see what you mean! Unfortunately this appears to be entirely an iWeb issue rather than a Nabble one.
From what I can make out from the HTML code, your whole site using using click and dragging techniques. On every page I looked at there appears to be a number of over-lapping layers so that while you may be able to see your forum, it, effectively, is covered by other layers. It looks to me as if you have used techniques that you may be able to get away with when working with desk top publishing software and expect to print your document but do not work when creating a web page.
One puzzle is where the embedding code is that I would expect to see somewhere in the code of your Message Board page. It is not there - anywhere. That suggests it is being loaded by some script on the page. In short, I have yet to work out how the page is even loading what you see.
Put another way, this problem is definitely one for iWeb support.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.