Cannot create Dropbox Data Source

I tried linking RDM to Dropbox without luck. First I tried authentication with the current session (client v3.0.3) and then I tried with the setting "Manual authentication" but no screen to enter the password is shown.

I have Windows 8.1, RDM v10.0.4.0 and Dropbox v3.0.3 and this happens on both 32bit and 64bit executables.