My wife S., a software engineer, just helped me solve it. Interestingly, it is a problem with my university's file server system, not with Blogger. (Blogger, I forgive you and I'm sorry I thought you were buggy)
Here are the details, for the techies in the room (and for myself, as a reference in case I have to deal with the problem again):
First, a description of the problem. When I try to post, Blogger gives me an error that looks like this:
450 Cannot open or remove a file containing a running program archive_11_01_2005.html
The file mentioned by the error is usually an archive file, but sometimes I also get the main "blog.html" file for the front-page of the blog. Clearly, since HTML files aren't exactly executable programs, what must be happening is the archive file is stuck in the middle of some kind of process, and that freeze is affecting all of the other processes Blogger needs to perform to put up a new post or publish a comment.
As I learned from attempting to erase the same file in a DOS FTP client, the file is actually an error generated by the university's server, and is only relayed by Blogger. While this error is happening -- which lately, has been most of the time -- I can't make updates or changes to my blog Template or blogroll (hence my very stagnant blogroll). Also, new posting may or may not work. And comments may or may not work.
Second, Google it. S. did a search for "Cannot open or remove a file containing a running program" at posting.google.com. From the results, it looks like it is an error that is unique to AIX Unix servers -- some kind of file corruption problem. The techies seem to indicate that the only way to solve the problem is to delete the file.
Third, go to Unix. S. taught me a couple of Unix commands I hadn't known. One is the command to see what processes are currently running on your server ("ps -aef lgrep [userid]"). When you run this, you see lots of activity, including recent attempts to post as well as FTP demands that are clearly people attempting to comment over the past couple of days.
Then, you can kill any stuck processes with a simple "kil -9 [process number]" command.
But actually, while it is hella cool to know how do this, it doesn't solve my particular problem. What solved it finally was simply renaming the problem filename ("mv [filename] [new filename]").
As soon as we did that, 11 halted comments from yesterday's appeared instantly, as did the post I had written earlier this morning.
(Incidentally, all of the above will be relevant only to people who are running their blogs off of a university server or other host. It won't be relevant to people with "Blogspot" or "Typepad" blogs.)