So, you have installed OS X Lion and for some odd reasons Dropbox doesn’t work correctly. What you need to do is to download the latest version of Dropbox, 1.1.35 is the current shipping version. If for some reason the shipping version is not working and you feel a little bit adventurous you can download the latest forums build; 1.2.16 is the latest build as of July 19th, 2011 and it is Lion compatible.