Khajiit just ignored that message. Seemed to log in fine despite it.

I had this happen the other night after I'd been playing and was closing down ESO for the night-- when I backed out of the character selection screen and closed the server selection screen, I saw the message had popped up on top of the launcher screen, but I don't know how long it had been there and it apparently didn't affect my gameplay. This was during the early AM hours of Monday morning before the servers were taken offline for maintenance.

This morning I was able to start the game normall after it patched itself from the maintenance, and cycle through all of my characters on both PC servers to get their twice-daily mails, with only the (now) usual problem of getting the "inbox full" message on most characters and having to run to the outlaws refuge to force a second mail check to get everything. But when I backed out and closed the game, the patch manifest error message was sitting on top of the launcher screen again with the "start" button replaced by "repair." It actually popped up about three or four times in a row, because each time I closed the popup it would pop back up after a fraction of a second. After the third or fourth time it didn't pop up again.

I might add that I've gotten this message once or twice in a blue moon over the last several years of playing the game, and it normally goes away by itself without any need to repair the game. The only reason I mention this is to say that it doesn't seem like the game actually needs to be repaired. If you click on the provided link at the end of the message to see the information about what to do, I think there are two or three things which are recommended to try before doing a repair of the game.

Anyway, I closed down ESO and Steam, rebooted, and restarted the launcher to see if the message would go away, and it came up before I could start the game. I closed everything again but didn't reboot, restarted Steam and the launcher again, and everything looked normal. So it seems to be coming up with much greater frequency than it ever did before, but it doesn't come up every single time for me. I haven't tried again yet this afternoon to see whether it comes up or not.