sansa e250 shutting down on rockbox, but OK with original firmware

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I recently picked up a sansa e250 (v 01.02.18A), rockboxed it on 1/31, and loaded a bunch of files (mostly FLAC, a few mp3s). 

It seemed to be working fine, but today, after about an hour of playing it shut down.  It was running rockbox.  It wouldn't boot up again at first at all, but after a few minutes it booted up again, and shut off after a few minutes (rockbox).  After a few episodes of this, I rebooted in the original firmware, and it played OK.

Does anyone have any ideas on what to do?  I'm going to run chkdsk and see if there's any disk issues, but the fact that it would play on the original firmware suggests that it's not a disk issue.

Thanks in advance for any assistance.