Well, it seemed to have worked this time. In my attempts, I had added the --config_file=bulkloader.yaml parameter, which was not needed.
So, now I have downloaded the data. I am again stuck at the error: "app "dev~myapp" cannot access app "myapp"'s data -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.