SiteAssist Pro will create pages derived from a template. This is what dictates the editable regions. When you are working with a template you will only be able to alter part of the pages that are within the editable regions. The editable regions should be labeled with tabs to let you know where they are. Within these regions you can put your cursor in and add content. However you will not be able to add content that is outside of these regions unless you are making a global change to all of the pages. To do this you would edit the template file directly, you can make changes to any part of this file.
In the image you have labeled failed you can see that you are selecting the entire content div, but the editable region is only within the content area of this div beginning after the editable region on line 264. From the beginning of this editable region until the end of this editable region you can alter any of the content, but not outside of it.
