So apparently, either I can "publish" from work but not from home, or I can publish during the day but not at night. Because for the last two nights my attempts to publish from home have led to error messages, but I can go to work the next day and, with the same post, immediately publish successfully.

For you non-blogger/blogspot users: "post" means that you save what you've been working on, but new material--content, or changes to your template (layout)--doesn't actually show up on your blog until you "publish".