I had this problem when updating on a PC with Windows 10. Using the offline installer did not help. Using an earlier version of DropBox, it installed, but then indicated I needed to update to continue. Finally I completely uninstalled the program using CCleaner (great program, BTW). I then cleaned the registry, ran the cleaner, and restarted the computer. At this point I went to dropbox.com, signed in, and hit the "install" link. Everything went smoothly from there and the latest Dropbox is installed and syncing fine. Hope this helps someone.