If you were not able to backup before DL, you can try the normal uninstall and your other game saves should return after new version is applied (worked for me as the AC4 DL corrupted my Uplay). If you already have Uplay on your PC, I would recommend making a backup copy to reinstall after game DL, as it may contain game saves for other Ubi games you own. You will need to update or uninstall/reinstall to the latest version of Uplay app from Ubisoft. When you DL AC4BF from Steam it will try to install an outdated version of the Uplay app on C drive. Uplay is Ubisofts DRM system, and may be updated multiple times a year.
