I’ve had this problem a few times now: I’ll record an activity on my 310XT, go
to upload it later, and the sync agent fails to pull the activity. My
suspicion is that there is a bad block in the flash memory on the watch, and
the watch hardware is old enough where it can’t work around it. I had this
problem with the old Garmin ANT+ Agent under OS/X, and I just experienced it
under Linux, with Garmin Forerunner 610 Extractor, a Python script that does a
similar job to the ANT+ Agent. What’s interesting is that the new script
always downloads all of the activity data, so I’ve been keeping the old
activities around, and I now know that the error occurs somewhere between
540k-584k of memory usage, and that the value equates to 24% of the watch’s
memory, based on what the watch says. So it’s a good guess that the watch has
about 2 megs of memory on board.