Webpost to Flickr fails with error message about checking "directory" setting

I added a flickr account to my webposting settings. However, when I attempt to send a screen shot to flickr, it fails with this error message.

There was a problem when Skitch tried to upload the file to the server.
Please check your "directory" setting

As far as I can tell, I have no "directory" setting. I can webpost to .Mac and Skitch.com just fine. Thanks for any help.