error generating navigation links - DocBook XSL 1.69.x + DocBook 4.4

Hey,

I'm trying to upgrade DocBook and DocBook XSL, and I've run into an error - 
the navigation links (to HOME, TOC, Next/Previous) are not generating 
correctly. The TOC link doesn't generate an image reference, and the 
Next/Previous links don't generate at all. I've read and re-read the 
documentation and I've set all the parameters that I can find - and nothing 
changes. DocBook 4.4 and DocBook XSL 1.54.1 seem to work fine together, but 
I'd like to update to a more current version if possible to have more 
options available.

Any ideas?

Thanks,

Tony