Does your database connection work? It tries to get the list of columns from the database table. If it doesn't have the table or the connection doesn't work then it won't let you add columns.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.