Sounds like when you clicked and dragged you picked up the letterbox frame lol.... That can be a real pain basicly if the whole area highlights in red then you have that selected, Try double clicking on another window and try again.
EdIT
Also you dont need drag them out the way! ... Just select say the Player file under the mainhud page in the tree view and toggle the visible button also in that pane .. that way you can just show / hide the windows as and when you want to work on them... (that is good to start off with, But if you are modding a mod you should turn back on / off any visablity settings you changed on the windows, as it can mess up the way the mod functions)