Perhaps you are not dragging the game to the applications folder. You are probably trying to run the Downloader on the mounted DMG, where there is no write access.

Message from UbiSoft: "Recent reports from our tech teams are indicating that Mac OS X 10.7.2 is breaking older versions of the Ubisoft Game Launcher, resulting in crashes when launching the game. You have to upgrade the launcher before launchi...

Message from UbiSoft: "Recent reports from our tech teams are indicating that Mac OS X 10.7.2 is breaking older versions of the Ubisoft Game Launcher, resulting in crashes when launching the game. You have to upgrade the launcher before launching ...

This problem may be due to a MAC OS upgrade that the GG Downloader not yet support. Open Preference > Security & Privacy, in the General tab is a setting called "Allow applications downloaded from:", select "Anywhere". or Ctrl+click or right click...