Image ad path is based on ad module directory

I'm having a problem on a test site that seems at first similar to the one reported here: #544936: Image ads do not display : wrong file path → - I just backed up the content of a live site onto the corresponding test site, prior to making a bunch updates on the test site, and now none of the ads are displaying because instead of having the image URL:

http://www.example.com/sites/example.com/files/ad.jpg

they have:

http://www.example.com/sites/example.com/modules/ad/sites/example.com/fi...

However, what was causing that person's problem can't be causing mine, because I don't have any sort of module archive on my site. I also looked the other issue linked to from there - 🐛 don't store complete redirect URL in database Closed: outdated - and tried what one person there suggested - editing each and resaving it - but that made no difference.

I checked the ads table in the database, but I'm not sure what I'm supposed to do to the redirect paths in there =. They're all in the format http://www.livesite.com/ad/redirect/299 (or whatever number) and while I did try changing a couple of them manually to http://www.testsite.com/ad/redirect/299, it didn't make any difference - the image path that turns up in the actual HTML of the site remains the same. I don't even know if the redirect paths are relevant to this, because the redirects seem to be for the URLs, not the images.

I also checked the ad_image table and the files table, but couldn't spot anything problematic in there.

Does anyone have any idea why this might be happening? The ads on the live site still display fine, and I copied the database tables over exactly - nothing else on the site broke, so it's not an overall file system problem. But for some reason, on the test site, the ad module is determined to make the image paths relative to the ad module directory.

This is really urgent, as the changes I'm supposed to be making need to be reviewed by the client tomorrow and go live on Friday. And they aren't going to be happy if none of the ads are showing up. :-(