Posted successfully and successfully approved are 2 different things. Posted means it likely went into the queue for webmaster approval. What makes it past his/her quality control and actually gets approved and placed into the comments section is the difficult part. Many blogs are abandoned and it will never get approved, many don't get approved and even for the ones that may, it may take them a week or two to get to your comment to review and approve it. You can't just check an hour later, not see the comment there, and say it doesn't work.