1 pixel gap in IE6

I'm new to CSS and am working on a naviagtion menu.

The problem I have is not with the links themselves or the hover effect, but with the background to the links.

I have a blue border set but in IE there is a 1 pixel gap to the right of the navcontainer ID but not in firefox....you can see it here :

http://www.housekeys.co.uk/hk_navbg.html

Can anyone offer any ideas why?

Thanks,

Robin.