hey mate ,
you can download software upgrade on garmin website
on the water
chartplotter
find 451 chartplotter
right hand side will have software (follow download instructions make sure you save before running wizard will guide you to sd card copy)
put sd card into gps450 holding power button and up arrow ( this will direct unit to sd card slot )
unit will display holding ( can take 5 minutes to run )
problem should be solved and latest software installed
wayne Qld garmin marine rep