Directory cannot be selected as Document root

If a dialog box with the text "The chosen user does not have the executable right for the selected folder!" appears when you select a directory, then you have probably selected the value "Unix users" in the "Run servers as" section of Setting > Ports & User and are trying to select a subdirectory of your user folder.

Change the value of the select box to "User USERNAME". Save the changes by clicking the "Save" button and then select your desired directory for the Document root of the host.