Starting from version 3.4, Linden Lab's Second Life Viewer can no longer connect to a grid of your choice (they have removed the '-loginuri' command).
This means if you use Virtual World Starter, or even just shortcuts to log into a non-Linden Lab grid (for example, a local opensim for testing), the last official viewer that can be used is 3.3.4 (just make sure that you have auto-update turned off, and in the future, changing the channel may be required to continue to log into their grid), otherwise the only choice is to use a third party viewer.