I would guess you lost your preferences and that is the name of the game with the NVFS system. Sometimes it is there and sometimes it is not there. Let me reword it - most of the time it is there and sometimes it is not.
You can restore the preference file by syncing back to the device the file named: Saved_Preferences. I would also consider installing Reset Doctor from Hobbyist Software,
http://www.hobbyistsoftware.com/reset-doctor-more.php. This application monitors the DB cache and clears it at the user specified level and it also locks the preference file and keeps the exchange manager clean.
Ben