“GPSMAP 276C software version 4.00 as of March 23, 2006” Strange it wasn’t there last night? 
http://www.garmin.com/software/GPSMAP276C_400.exe
• Added Iceland time zone.
• Added support for latest Garmin map technology.
• Added ability to select units used for displaying vertical speed.
• Added ability to quickly select entire track for use with TracBack.
• Improved voice guidance for road routes.
• Improved Compass page in Automotive mode.
• Improved Sonar page.
• Improved Find menu.
• Improved map selection when changing usage modes.
• Corrected issue that could prevent some message log filter settings from being saved.
• Corrected issue that could cause unit to shut down when using the Highway page.
• Corrected issue with waypoint timestamp updates when transferring from Mapsource.
• Corrected display of 'L' symbol in Turn data field.
• Corrected display of 'Route Truncated' and similar messages when using USB.
• Corrected display of cardinal direction on map page when measuring distance.
• Corrected duplicate waypoint creation with GPWPL NMEA sentence input.
• Corrected hilight movement problem on proximity waypoint page.
• Corrected invalid display of Next Turn data field
Just as a precaution, back up your waypoints, trails and routes if you want them before loading, ok
http://www.garmin.com/software/GPSMAP276C_400.exe
• Added Iceland time zone.
• Added support for latest Garmin map technology.
• Added ability to select units used for displaying vertical speed.
• Added ability to quickly select entire track for use with TracBack.
• Improved voice guidance for road routes.
• Improved Compass page in Automotive mode.
• Improved Sonar page.
• Improved Find menu.
• Improved map selection when changing usage modes.
• Corrected issue that could prevent some message log filter settings from being saved.
• Corrected issue that could cause unit to shut down when using the Highway page.
• Corrected issue with waypoint timestamp updates when transferring from Mapsource.
• Corrected display of 'L' symbol in Turn data field.
• Corrected display of 'Route Truncated' and similar messages when using USB.
• Corrected display of cardinal direction on map page when measuring distance.
• Corrected duplicate waypoint creation with GPWPL NMEA sentence input.
• Corrected hilight movement problem on proximity waypoint page.
• Corrected invalid display of Next Turn data field
Just as a precaution, back up your waypoints, trails and routes if you want them before loading, ok
