Um, I had yet more problems logging in with my Yahoo email on the iPad a couple of weeks ago so I contacted one of the Flickr support 'heroes' He gave me a couple of options, one of which was to transfer my sign in over to a non-yahoo email. All done in a matter of minutes and now works perfectly. That's the end of Yahoo for me! You'll still see the Yahoo login screen but can just use a non-Yahoo email in it.