WordPress MU

Hello.
I've set up a MU installation for a fanclub, and everyone uses the same theme. A couple of days ago a caching plugin went haywire, and I removed it, which caused everything to crash, so I just upped a backup of the contents of the db made earlyer that day, before the plugin issue.
Now it seems like the background graphics in the theme on the memberblogs doesn't wanna show at some times, I've seen the problem after midnight the last 2 days now. They seem fine in the daytime though. It's the strangest thing. The same theme bacground graphics are fine at the same time on the main blog, its just the memberblogs that have this issue.
Any ideas how to correct this?
The setup is only 4 days old, and have just gotten 2 memberblogs yet with a few posts each. I guess I could delete those blogs after backing up their contents, make new ones for those 2 members, and recreate their posts, but I'm not sure that'll fix it and it's not a viable solution if the issue with the theme happens to new blogs in the future either.
Would really appreciate some expert opinions on this.

Check it in other browsers.
Doublecheck to make sure the images are there on the server and accessible via the browser.

The images are there, the main blog is showing the theme as it should be with no issues any time. It's just the memberblogs that have an issue with images, both theme graphics and blog entry images, and it's intermittent, not constant.
Running one of the blogs through browsershots now to see how it looks in a couple of dozen popular browsers and versions.

Are the memberblogs using the exact same theme, or a second copy?

Exact same theme.
I've been taking a closer look, the graphic representation of functions on buttons in the blogs admin pages are missing as well. On the write screen when making a new post f.example, the buttons on top of the write box doesn't have the graphics they have on the main blog. They function as normal, but all graphics are gone.

By the way, browsershots confirms the issue in msie, ff, opera and safari in all versions tested, and likewise the main blog is confirmed to display properly.

Then there's something up with your server or the way you transferred the files.

I'm suspecting hotlink prevention may be the culprit, it was working fine until the server provider recommended I activate that because of the 68GB of traffic the previous day, which was before the WPMU site was opened.
Maybe it'll work with hotlink prevention turned off for graphics, and still on for video.

Yep, it;s hotlink protection.

If you have that much traffic, it might not all be that. It's pretty easy to see if someone's linking your graphics directly. There's plenty of other reasons you can ramp up that much bw.

Like splogs trying to sign up, for instance.

Real numbers, and about 40 000 visitors in the last 20 months on the old setup.
That load was the day before the wpmu went online on the site so splogs wasen't an issue, no registering available in the old setup. The site is associated with a TV broadcaster here, and several of their program hosts, hence the traffic.

Seems like its resolved. The intermittancy of the issue may have been due to list variations in some dns nodes or something, not too sure about that but there's probably a natural cause for it varying the first couple of days after changing hotlink settings.
Typical me to link any issues to the most recent previous issue to be solved, seems unrelated to the caching hickup now. :P
Thanks andrea.