James,
Your log file indicates that the file exchange request failed with an I/O error (-36).
2010-11-07 16:47:07.494 -0800 Failure Failed
2010-11-07 16:47:07.494 -0800 Details cannot swap files
2010-11-07 16:47:07.494 -0800 #debug# IO exception
2010-11-07 16:47:07.494 -0800 Details Path: /Volumes/x/Backup.quanta/layer_scribble.index
2010-11-07 16:47:07.494 -0800 Details Other: /Volumes/x/Backup.quanta/layer.index
2010-11-07 16:47:07.495 -0800 #debug# API: FSExchangeObjects
2010-11-07 16:47:07.495 -0800 #debug# OSErr: -36
Since there's actually not much I/O involved in exchanging files, and it happens every time QRecall attempts to exchange files on that volume, I'm going assume that it's a bug in the implementation of the filesystem.
I'll add it to the list of anomalies to investigate, and I might even be able to develop a workaround, but I would suggest that you begin by contacting the developers of Macfusion, and pass along this information.