I'm sure it is this empty div that is the problem.
<div id="right-half"></div><!-- #right-half -->
With the styling
Safari and Chrome have problems with negative z-index and so the div is effectively 'covering up' part of the sidebar so you cannot access the links. If you try a link towards the bottom of the sidebar (that is below the offending div) you will see that these links work.
I've found that negative z-indexes are unreliable across browsers and I tend to avoid them now, using 'stacks' of positive ones instead