I just installed some Windows Updates from the website and after that, I was getting the same error message. I uninstalled the updates (they had to do with Internet Explorer I think, and I don't use that anyways...), and after that iTMS started working for me again. So you might want to check if your computer has installed the Cumulative Security Update for Internet Explorer for Windows XP Service Pack 2 (KB834707) and try to uninstall it and see if that helps.