I've been getting this error continuously since the patch yesterday (on NA) when trying to login to more or less all of my characters. I login without issue every time, I click the specific character and hit enter, the loading screen comes up, the little ESO icon in the bottom-right starts spinning but then stops spinning (apparently frozen; if you click on the ESO window while it's not spinning, ESO stops responding), and then it either starts spinning again and loads the character almost immediately (5% of the time, tops), or I get the error in the subject line as I get kicked back to the initial login screen. Up until this patch, the spinning ESO icon freezing up during the load screen has been a normal occurrence and didn't seem to impact anything, however.
Can someone from ZOS confirm if this is a known issue, as I've tried everything short of re-installing Windows (not going to happen) so I believe I can safely assume that this is an issue somewhere server-side or in between. Let me know if you want a DXDIAG, TRACERT logs, or any troubleshooting info from my side. This is seriously impacting my ability to log in, let alone play, and I would like a solution (a workaround would be just fine as well) ASAP.
About to try logging in through a VPN connection to see if it makes a difference, but since Early Access, I've had very few issues with lag or overall latency, so I doubt this will make any difference either.
We have contacted our Customer support team to help you solve your issue.