I don't have a 64, but thought this was interesting...
http://forums.groundspeak.com/GC/index.php?s=7c8a266282d0ca0bae607f14e4603bee&showtopic=325879
QuoteI had spoken to Garmin tech support about this, and they suggested that a corrupted map file could cause this. In my case, removing the "My Trails" map from gpsfiledepot.com cured this condition. I have downloaded the updated "My Trails" map but it does the same thing. I also noticed that when My Trails was enabled, it disabled the Garmin 24k Topo map and would only show the generic basemap instead. I had emailed the author of My Trails, but I have not yet seen a resolution to that. I have no such problems with other maps from gpsfiledepot, just this one. But taking My Trails off the device cured this issue of the zoom data fields getting corrupted and crashing the 64s.