Perhaps not pertaining to many out there but I was having this error with Windows Live Writer not being able to download (refresh) my site's theme and I've seen a few others with the issue (though perhaps different circumstances).
After some consideration it dawned on me that I'm now using a custom version of the Front Page Category plug-in to control which categories will show on the site's main page. Of course I've excluded the "unassigned" category so WFW's efforts to make a sample post are in vain since it won't show on the main page. Which is clearly needed for WFW to then "download theme" successfully.
After I tweaked the category exclusions so the "unassigned" category would publish to the main index page WFW successfully retrieved the site's theme.
Problem solved.
