Garmin 305 software problem.

The 305 has limited memory and the GPS data it records can get big quick.

In order to keep recording new workouts and maintain the important data from older workouts, it will throw away GPS data for older workouts to make room for newer data.

I'm not sure if the criteria is workouts over a certain date or number or if it's based on available memory. Given the excellent design of the unit, I'd say it's probably some sort of combination.

It's important to remember to delete workouts occassionally from the unit. This will also make uploads to online services like the Route Tracker and the training logs much quicker.