I've never sed that unit but ive seen it used by a few co-workers and they are great.
sounds like you should try reinstalling all the software and doing a reset on the GPS unit.
Ive never heard of this problem though so i cant be sure this will fix it.
if that doesnt work i suggest bringing it back for another.
GPS is so helpful for me. I run my setup with a Dell Axim X30, Deluo reciever, and iGuidance software.
my mom just got the Globalsat 359W
Garmin is one of the best GPS makers out there.