CSS not loaded on some PC's for BSP

We are just about ready to go live. Our users are out there testing. For the majority of the users they see the BSP that we designed exactly as they should. For a few others when a screen comes up it appears without the CSS stylesheet and the formatting looks off. It's like the MIME object isn't found or active. Two people sitting next to each other see the same screen completely different.

Anyone seen this before, or know what settings are causing this?

Anthony