I can't enable Dropbox Backup as there's a conflict with iCloud.

[Jamie P.8]

I am trying to set up Dropbox Backup, and when I selected Desktop, Documents, and Downloads to be backed up, it told me to disable the iCloud backup of these folders. When I attempted to do that, it said all of my files would be deleted from my computer and stored in iCloud-and any new files or folders would not be stored in iCloud. I want to use Dropbox to backup these files and folders, but do not want all of those files to be deleted from my computer. Any other way to do this?

[Mark]

Unfortunately you can only have one or the other - iCloud or Dropbox on a folder. 

So, if you want Dropbox to do it you need to download them all locally first and disable iCloud.