I followed all these steps on the KB page and nothing worked. Now the game is telling me I do not have enough space. I have over 30GB free space on my HD.
I have a manifest error too.What has worked in the past and what works for me now, is running the game via a shortcut to the eso.exe directly, bypassing the launcher.
Don't repair it is a waste of time. This error has been around since release. Launch the game from eso.exe and you should be able to log into the game. Only use the launcher for updates.
If you open and close the launcher a few times you will get a good launcher if you insist on using the launcher to get into the game. Most of us never use the launcher except on patch day. Just make a shortcut on your desktop to the eso.exe and you are good to go.
As posted above, when you get the error don't repair just close the launcher and open it again. It may take 2-3 tries but eventually you get the play button. This often happens after a new patch, but clears up on it's own eventually.