Is this your first time here?
Login is your King County email address (all lowercase!) (firstname.lastname@example.org or email@example.com)
If that doesn't work, try using your network login followed by @kingcounty.gov, like this:
When you log in for the first time, you will land on a profile page. Enter your name and your email address, then scroll to the bottom and click Update. Be aware that your email address might be different from your login for this site.