Originally Posted by
steveholt
Anyone else having trouble logging in on the new version of the site? Old site works fine. New site says "Whoops! Please enter valid login credentials to continue," even though I'm entering in the same credentials that work on the old site. DL twitter says that it's a known issue.
There was a sub discussion as part of a more generic discussion about the new site:
Did Delta Just Overhaul Their Website Again?
tldr try deleting all your delta.com cookies.