This is happening to me on Windows 10 Pro 64-bit. When I first installed Dropbox 3.14.7 I thought it it was well-behaved, because it offered an option to disabled "Start Dropbox on system startup". But that doesn't work.
I have certain drives that aren't mounted when the system starts. I have moved the Dropbox configuration files (via an NTFS symbolic link) to that drive, but I make sure that I mount the drive before starting the Dropbox desktop application. I have disabled "Start Dropbox on system startup".
Yet still when I boot Windows 10, Dropbox throws up a dialog informing me that it has failed to start. *I had told it not to start automatically! Of course it will have a problem---I haven't mounted its settings drive yet. *But I told it not to start!*
If Dropbox has a "Start Dropbox on system startup" option, it should honor that options. Don't control my system while pretending to give me options to disable the software. Please tell me how to *really* stop Dropbox from starting automatically, even the secret whatever-it-does-to muck-around-with-my-system, or I am removing the software from my computer. Thanks.