I'm saying that Dreamweaver has to be able to browse the files that are uploaded using the url you entered. However you need to get them in sync, that is what you have to do.
Dreamweaver is going to FTP files up to your server and try to browse them. It will FTP them up to the directory specified as the root, and browse them using the url specified as the Web URL. If it can't do that, then it won't work.