99% of the time that happens, it's because the person selected the Game Profile, in the Game sub-menu from the Inner Space menu, instead of their Character Set from the "ISBoxer Character Sets" sub-menu (also in the IS menu!)
If you DID select the Character Set and only one launches, you can usually look at the main Inner Space console to see what ISBoxer was doing and perhaps failed to do. See
http://isboxer.com/wiki/Console. If you can't figure it out from looking at the console, that page tells you what to do to copy and paste from the console. Get me the bottom 5 lines or so from trying to launch your Character Set.
Also... depending on the launcher you're using, it may remain open after the game launches. If it remains open, ISBoxer cannot launch the next one. There is an option in the Station Launcher to prevent this. Make sure that in the Station Launcher options, "Exit Station Launcher when I play a game" is checked. To find this option, select Preferences from the Station menu (in the Station Launcher) and it's in the "Startup / Shutdown" category under "Shutdown options". This is necessary because Inner Space will need to launch the Station Launcher once per account. Also, make sure the Station Launcher is closed before launching Star Wars Galaxies through Inner Space.