Mac OS X 10.4 Tiger provides the ability to reopen applications that have unexpectedly quit. On the first attempt, if you choose to reopen an application that has unexpectedly quit, it should open normally.
However, if it unexpectedly quits a second time, the Finder will offer to open the application using its default settings. If you choose to do this, the application gets temporarily set back to the original condition in which it came (before you did any customization). If you then quit and reopen the application, it will open with your normal user settings back in place.
If Backup 2.0.x unexpectedly quits twice in a row in Mac OS X 10.4, the application may open in Trial User mode on your second recovery attempt. In Trial User mode, Backup doesn't have access to your .Mac preferences. If this happens to you, just quit Backup and reopen it again to use your normal settings. You may see an alert message that asks if you want to save the new settings. Click No to use your old settings.