this means that the upload folder on the live server does not have appropriate permissions for uploading a file.
you will need to modify the upload folder permissions on the live server to allow write access.
in Dreamweaver, open the file panel (Window -> Files) in the file panel, change from Local View to remote view.
In remote view, right click the upload folder and select Set Permissions. set the permissions level to 755.
NOTE: some hosts wont allow Dreamweaver to make this change, you may need to use a dedicated FTP client like FileZilla.