I saved a map, and when I went to open it back up, I was prompted with a dialogue box saying Handle Bad layers. What does this mean? The map was fine when I saved it.
It means the layers cannot be found anymore. Maybe you moved the .qgs map file (so relative links are broken) or you moved/renamed the layers, or the database connection cannot be re-established.
You should use this dialog to point to the proper layers, else they will be removed from your map (leading to lots of frustration later on)