Not all icons show up in Openbox

[Yes]

I installed Ubuntu server in VirtualBox, and I put Openbox on it. I tried setting the icons by putting 'gtk-icon-theme-name = "Nou"', and some of the icons show up but about half of them are a picture of a sheet of paper with a red 'x' in the middle. Are there any dependencies for using GTK icon sets? I installed GTK2-engines, but is there anything else?

Thanks.