**This is the problem. When the iPhone shows up in Windows Explorer, if you double click it immediately, it will show up as empty. Normally, double clicking your iPhone in Windows Explorer should show an "Internal Storage" folder, and inside it should be a "DCIM" folder. For some reason, it takes up to 2 minutes after plugging in the iPhone for these folders to appear. Dropbox can only import files when these folders are working properly.