Many of you have noticed by now that MarsEdit is not working well with Flickr. I'm sorry about the sudden failure of the Flickr support in MarsEdit. Flickr made a change to their API and I did not make the required changes to MarsEdit in time to accommodate the change.
I'm working on an update to address the problem, but if you'd like to try it out ahead of time you can download and install a beta release version of the app:http://www.red-sweater.com/marsedit/MarsEdit3.6.5b3.zip
I hope this will get you back on track with Flickr support in MarsEdit until I'm able to get an official release out.