If you experience a problem with your connection to your shared database, the Connection lost dialog will show up. You can choose to Reconnect, Work offline or Close database. Most of the time simply reconnecting will fix this problem, if that's not the case you will have to choose between Work offline or Close database. Pick Work offline if you want to make sure your changes are saved. If you think there is nothing to save just pick Close database. If you choose to work offline, JabRef will convert the shared database to a local .bib database. Since you are no longer working online, but instead on a local database, you will have to import your work via copy and paste into the shared database. However before you import it into the shared database, make sure to check if changes happened during your offline time. Otherwise you might override someone else's work.