[SOLVED] 3.5.2 Cat & Menu Bar background displaying at 100% (Fixed width 900px)

Hi Guys,

Just downloaded Atahualpa (3.5.2) to check it out against WP3.
I've set Atahualpa to a fixed width of 900px however the category and menu bar background colours are displaying at 100%.

Link: http://mickregan.com/isic/

No plugins applied - just the basic theme.

Can't pin down the cause using Firebug unless i'm missing something?

Any thoughts welcome,

Thanks,

Mick.