“invalid post id”

I am a Mac user with a new WP website. I’ve been posting entries from MacJournal without issue.

I uploaded one entry several times, tweaking it trying to get it just right, resizing the photo between uploads. Then, all of a sudden when I tried to upload for the 4th or 5th time, I got an error message saying “invalid post ID”. Nothing seems to help. I’ve quit and restarted everything several times, etc. to no avail.

I saw a forum entry on WP.com by a guy with the same problem when posting to a WP hosted blog. Mac, MacJournal, several uploads and then the sudden error message. No help posted for him yet. When I posted that I had the same problem, I was directed here, because my blog is not hosted at WP.com. Any ideas?