Category links problem

I’m not exactly sure when this issue popped up — I seem to recall things working fine back in WP 1.5, but apparently something with the latest installations introduced the difficulty — but I just realized that none of the category links in my posts work. Whereas before they defaulted to the index page with the appropriate category number (frex, http://www.wesoteric.com/index.php?cat=13), now they default to a category permalink structure that I haven’t specified in the options menu (see http://www.wesoteric.com/category/blog/audio/) that simply brings the viewer back to the main page. The dropdown categories menu in the sidebar still works and goes to the appropriate pages, though.

Any ideas? Your input will be much appreciated. 🙂