Can you try having an open hyperterm (capturing the session) while trying to sync via USB (or ethernet)? This way, any kernel error messages from a memory error or program crash can be captured and reported.

If you are running out of memory during a database rebuild, there might be a way to fix it - by turning on the swap before syncing. This might be rigged either with a hijack program run when connected to AC (you do not want swap on while in the car, I assume), or manually doing:

q #drop to shell
swapon /swapfile #turn on swap
exit #exit shell
#sync with emplode