The problem in detail is here. The quick summary is that every time he tries to get to the Edit Template page, it redirects immediately to a blank page, so that no edits can be made, and the template can't even be replaced with an older backup.
This has been going on since Blogger stopped access through the old interface several months ago. No support email gets any response, and repeated posts on the forum don't either. Many other reports can be found in the forums concerning people who can't get any help from Support.
If any of you have any suggestions, or especially if you have an inside track to some human being at Google who might help, we would really appreciate it. It's time to change the masthead and update the listings for our books.