Yes, I am encountering the error again as well.
Yes, I’m almost tearing my hair out beacuse of this “You can’t log in as XYZ from that IP address” error. Right now I tried clearing browser’s cache, an anonymous window, even an alternative browser (IE), nothing worked. I have also seen this error on my phone’s browser. Right now, I even had to connect via the phone’s “internet sharing” option to log in!
Try using your complete email address to log in: jklaas@domain
If that doesn’t work, try omitting the @domain: jklaas
It is a known bug (or feature) of Discourse forum SW.
It helps to press “Login” button or “Enter” many times (again and again) for correct login (after typing correct username and password).