This message is about the database connection manager in Power*MatchMaker (this section of the forum deals with the MatchMaker, not the Architect).
The dialog in the screenshot certainly looks similar to the one in Power*Architect--in fact, it's produced by a library we share between both apps--but there is no Login button in the Architect one.
A "Login" operation wouldn't make sense in Architect. The closest idea to "Login" that makes sense in Architect would be "Add to DB Tree". Currently, you do that by right-clicking in the DB Tree and choosing your connection from the "Add Source Database" submenu.