Hi, Doug. Not sure if this is possible for you, but I once had a course kind of wig out on me (it went to a completely blank screen when I tried to enter the main course page as any user type) and I used the navigation block to troubleshoot my way back to getting most of it salvaged; I still am not 100% certain why it happened, but I think for me, it was some conditional acitivities settings that were conflicting somewhere. At least, that is what I thought at the time. It also, coincidentally, happened for me at a time when we moved repository servers. Maybe there was something to that, too--can't remember how many things I changed before I finally got it working again.
In any case, here's how I accessed what I needed through back doors: I had navigation block options enabled in full on the site for me to get to places, down to the activity level, inside courses without having to go through the course home page, and I revised settings and played with using single activity backups to restore the parts I most needed in a new course from there until I was able to change enough settings/go back in time enough with some of the content to make the old course work again. Do you, by chance, have that ability to go through back doors in your course using the navigation block from the front page or from your profile page?
If you do, and you have repository content in the course somewhere, I'd also use that back door access to try to get to the repository resource settings page to make sure it is pointing to the right server location if you recently changed servers for your repository, or something like that might have caused the error for the course.
Hope this is making some sense. In a different thread, you asked what sense it is to have backups stored in the course backup area if you can't get to the course backup area through the normal paths (as in a situation like this where the course administration settings are not available to you from the course main page). Here, I'd also have to say that the nav block came in handy as I was able to get to that area (course administration) from the nav block once I found my way to at least one of the activities in the course using the nav block on my profile page. From there I could access the course backup files.
Totally understand that frustration, and concur with Ken that doing a combo backup in future might be a good idea for you. To be completely safe, you can ask the automated backups to send the files to both a designated backup server folder location and your course backup area. The main advantage to having them available in the course backup area is if you have other teachers on the site who need to access their course files and/or try to troubleshoot things they did in their own courses without having to go to the site admin/server admin support to do it. Hope that makes sense.