Sansa Clip Zip bookmarks stop working

[Tom Cunningham]

My Sansa Clip Zip died recently (wouldn't power on).  I plugged it into my PC and it managed to recharge, but since then when I try to use a bookmark, it simply returns to the previous screen without going to the bookmark destination.  If I select a bookmark from the bookmark file associated with an audio book, it says "nothing to resume."  The content of the bookmark looks OK, e.g. it's the right book, chapter, and time offset, and Rockbox still creates bookmarks according to my settings.  I tried reflashing the firmware (3.13) but that didn't help.  Any ideas out there?