I have gotten that a few times too. been wondering if it has anything to do with the length of the persons blog entry itsself. maybe the main blog entry is too long so the comments end up with very little space. When someone commented on one of my entries I kept trying to post a sentence and that same error message came up so I shortened my reply to just a few letters. and it went through. Try posting just one or two letters and seeing if it goes through.