It clears itself in 15 minutes, IIRC. You should still be able to login via the front end, even while the board is closed for the upgrade, but filling in the CAPTCHA. (I'd have to confirm that.) I believe a successful login will clear that.
Alternatively, you can clear the xf_login_attempt table.
I cannot log in to the front end even though FF correctly saved my login info. It won't log me in.
So I use the /install/ url to do the install. It asks me for a login (w/ white background or the Upgrade System login)). FF correctly remembered this and I'm in. It then asks me a 2nd time (w/ a blue background aka Admin CP) and this is where the hiccup is.
I finally got in, remembered an old pw.
But what would have happened had I not remembered? Would I have to uninstall the board? Is there no way to recover admin pw's in such instances?
I'd reupload all files to ensure that everything is overwritten problem. If you still have problems, send me a PM with FTP and admin login details and I'll look into it.
Alternatively, assuming you still have the files from the previous version, you can rollback to that. As a further point, if you turn on debug mode in the config.php file (add $config['debug'] = true; at the end), you will still be able to access the board while the upgrade is pending. That should help let you try to deal with the logging in issues.
This is definitely an issue. When I get to that blue screen, it refuses my password, even though I 100% know it's correct. I can clear the login attempts table which unlocks the account, but I still cannot log in.
Login attempts on the "closed" front end are simply ignored and you get the login link again.
To be honest, I'm not really sure. I'm mid way through an import attempt (about 24% through the threads and posts stage, with over a million posts) so I'm not sure if it's possible to get back to that point without starting again.
I did wonder about this...when I first installed beta 1 I created a new admin account, with a basic password that differed from the one on my live site, then I tried an import from vB3.8. Although the import wasn't completed, the user table did import so my vB account became merged with the new one I created as they had the same name and email. The two passwords would have been different, and *neither* of them worked on that admin screen, but I do wonder if something got confused there somehow...though I can't think how.