Disable automatic updates

After you have done all those various things without any progress - such as gone through the registry and done all you possibly could to prevent the spate of dropbox 'failed to update' pop-up windows (eg...5 or 6 minimized notification windows that you see when you eventually come back to your computer after many hours) ..... then you can use 'Process Blocker' for Windows systems. That will sort it out once and for all. Once you install it, you just configure its blocked applications list with 'dropbox-upgrade*.exe' and 'dropboxupdate*.exe'. You can even disable the blocking notification. No more problem.