We just launched a new company site for a client. After chasing down some "OMG it looks wrong now!" complaints, we determined that the CSS (and some images, perhaps more) is getting blocked by their firewall. They claim this never happens to them with any other sites, but the effect is consistent across their network, and can't be reproduced outside.
It's not a very big site. Everything is being served from the same server, running a minimal PHP-based CMS, and the client never reported a similar problem during testing from our server. Is this likely to be anything we can fix, or is this solely a problem for their IT?