From the FAQ at the top:
Quote:
» How do I edit or delete a post?
Unless you are a board administrator or moderator, you can only edit or delete your own posts. You can edit a post by clicking the edit button for the relevant post, sometimes for only a limited time after the post was made. If someone has already replied to the post, you will find a small piece of text output below the post when you return to the topic which lists the number of times you edited it along with the date and time. This will only appear if someone has made a reply; it will not appear if a moderator or administrator edited the post, though they may leave a note as to why they’ve edited the post at their own discretion. Please note that normal users cannot delete a post once someone has replied.
Apparently it is not always and the limited time isn't specified as to hours, days, weeks.
I ran into this early on with a post only a day old and misspelled words, it had several post after it and that may be a key factor.