Moved site redirects to old site

I have a site that was started on a different MU installation (not mine), and was eventually moved to one of mine. The images moved with it, but they didn’t all show up in the posts. And the embedded videos didn’t transfer at all. So as I go through each post to replace the images or videos, after I do a few, I get a message that the page can’t be loaded because it has been redirected too many times.

The url shows as http://www.mysite.com/www.theoldMUmainsite.com/ I have contacted them and they don’t know what to do. They are more involved in marketing than in hosting technicalities.

I did a quick search on the database and came up with their name 47 times. In 3 pages and the rest were posts. The pages show (in the database) their url as http://www.theoldMUmainsite.com/?page=22, but that doesn’t show in the WP editor, it shows mysite.com/contact

I can’t find their site name in any post from the regular editor. Does anyone know how I can fix this, or what is going on?