After the patch successfully... Patched, I've been unable to log onto my SK account's knights while using my Steam client, which is making things very inconvient for me as I like to play on my alts more than my main.
Using SK's normal client fares no better fate, however, as I've attempted.
OOO, do your best in fixing this post-haste, you may lose over half of your playerbase from this error.
Happening to me as well.