Answered How on earth am I supposed to post a message on a member's profile?

Start a conversation: Go to their profile, and type in the box that says “Write Something...”

Reply to a post: Click the “Show Conversation” on the bottom of the post, it’ll take you to a new page with another blank box.

 

It requires a minimum number of posts to be able to post on walls, but I think you've reached that minimum. Not every member has their wall active, so it may not be possible to post on some walls, but most should now be open to posting.