I had a similar shutdown problem with my Curve 8300. Sometimes it would shutdown after the calendar synched, but usually it would shutdown upon punching the synch button. Erroneous instructions were given to me by the AT&T tech that caused me to have to restore the desktop manager so that I could properly delete it. Anyway, after a reinstall, it only worked once.

It turned out that the problem was with recurring Tasks. I deleted recurring tasks in both the hand held and Outlook and the synch worked fine.