Do you get the 404 on our 1.2.6 demo site? Or just on your server? What does the web server error log show?
ok, upon further investigation on my end it appears to be 302 errors according to the IIS log file for the website.
Its driving me crazy, I can't even add documents now, done a fresh install of ODM as well and still not working...
None of the issues I have occur with the demo sites, so I know its an issue at my end but I can't pin down the problem.
You could also try installing WAMP on your server and using apache instead.