Anyone ever run into this? I upload a website that I built for a client to my server/URL. Works fine, no problems. Then, I take the exact same source files, upload them to the client's server/URL (with a different hosting company), and all of a sudden the site starts to behave ridiculously...if you make a change and refresh, it doesn't show, within 30 minutes of putting up a background image it no longer displays in the browser...etc.

What gives? I know the HTML checks out. Any guesses? I'm at my wits end.