Flickr changed how you access your images in early September. So I’ve updated the plugin. You’ll need to have an “API Key” and a “Shared Secret”, now.
It is a good idea to put images on Flickr instead, or in addition to, stj servers. Flickr badges are cool, too.
Do not activate the Flickr plugin if you don’t have a Flickr account. You lose the ability to browse your blog’s upload folder while Flickr plugin is active, I still don’t know the fix.
Look here, see if you can find a fix, too.