Unknown error 3

I'm trying to synchronize between two machines, and synchronizing never completes, and 'error 3' is reported in the dialog box (that I pull up). I'm running Firefox 3.0.5 on a linux box (and also a Windows XP machine, but that doesn't see the problem).

From the log file (see below) it's having an issue adding a bookmark to a folder which is
in the toolbar folder. This happens with auto-sync and 'force download'.

The log file says this:
[2009-01-22 10:04:19] Creating bookmark start [EBEX Wiki](fq70kppf-c) ...
[2009-01-22 10:04:19] Exception in AcceptNodes: Error: Places error calling function insertBookmark() {
[native code]
} with args [696, {}, -1, "start [EBEX Wiki]"] Original error: [Exception... "Component returned failure code: 0x8052000b (NS_ERROR_FILE_CORRUPTED) [nsINavBookmarksService.insertBookmark]" nsresult: "0x8052000b (NS_ERROR_FILE_CORRUPTED)" location: "JS frame :: chrome://foxmarks/content/foxmarks-places.js :: Call :: line 100" data: no]
[2009-01-22 10:04:19] Returned error: Unknown error occurred (3).(3)
[2009-01-22 10:04:19] Will retry at Thu Jan 22 2009 10:19:33 GMT+0000 (BST)