Eugene1

How did you set up Apache and PHP on your computer?

Apache, PHP and MySQL was set by pack: “HomServ”.
I have used it for years without any problems.

OK. I have deleted ALL cookies in Chrome. No difference. I cannot login by Chrome, only by Opera and only to parent site.

That kind of sounds like the login loop of doom…

Yes.

Have you deleted all the cookies for that site?

I could not. Chrome never receive cookies at all. Opera, probably, have valid cookies only for main domain.
Possibly, cookies that WP attempting to send, have illegal char because of wrong localization.
Apache under Linux correct the char, under Window does not.

In any case, it would be reasonable to inform user about send cookie failure.

As far as I understand, it does not makes sense. In no way.
1) My firewall rules I know, and turning firewall off change nothing.
2) I don’t use IE.
3) “system-level within Windows rules” hardly can penetrate between server and browser. They communicate almost directly.

Also, sending cookies error might be catchable…
Or, at least seen in error logs.
But I have only this in logs:

127.0.0.1 - - [12/Apr/2013:14:09:05 +0000] "POST /wp-login.php HTTP/1.1" 302 -
 127.0.0.1 - - [12/Apr/2013:14:09:14 +0000] "GET /wp-admin/ HTTP/1.1" 302 -
 127.0.0.1 - - [12/Apr/2013:14:09:17 +0000] "GET /wp-login.php?redirect_to=http%3A%2F%2Fen.signals%2Fwp-admin%2F&reauth=1 HTTP/1.1" 200 2405

I have set up a new MSWP on hosting – no problems.
But under Windows 7 there is a problem with sending cookies.
Don`t know how to research it further.

I checked Chrome, but it is OK, on other sites it manage cookies correctly and show them to me.

Curtiss, thank you for advice!
But I cannot login at all from Chrome, while see front end of all sites.
And it write to me:
“This cite has no cookies”

It sounds like something is going wrong when setting the cookies for your subsites.

Yes.

Do you have any way to inspect the cookies that are being set to see if they match the location of the sites?

No.
I used Opera to inspect cookies. But in new Opera it does not work.
How would you advise me to inspect cookies?

I have almost the same problem.
But have you check if user granted access to the site?
Also, if you have 500 Error, show please your .htaccess file.