I expect that at the time you made the post you had or were very recently at the point of still being in the 5 post state. There is a short time period between going past 5 posts and having the system upgrade you to a full member with the new privalages. So for other people wondering you need to get to 5 posts and wait about an hour or so and then once you are able to post without the nag screen coming up about moderation then you ought to be able to modify your profile.