The browser and Flash Player versions will determine if the sign up box shows. The minimum requirements for using the CS Review web application are listed here https://csreview.acrobat.com/tech_specs.html. The Flash Player version the particular browser is using can be determined here http://www.adobe.com/software/flash/about/.
For trouble-shooting try clearing the browser cache and cookies. The steps for doing this vary by browser. Also clear the Flash Player cache from here http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager07.htm l.
If there are still issues please reply with the specific browser version and Flash Player version that is not working.
Ken G. Rice