The connection to the server was reset after trying to log as admin to Drupal I did upgrade on Drupal 7 and imported these sites and database from localhost to another server. On localhost everything works well, on the server I can´t log to Drupal as admin. After  entering password every browser shows similar message:The connection to the server was reset while loading page. When I want to change address in browser after that I have to delete all history, cookies, cache, etc., otherwise it writes the same message. I changed base_url, cookie_domain in settings.php, deleted cache and session tables in database. It didn't help.

Notes:


Putting /?=admin doesn't work, I am redirected to homepage, even on my localhost page where I can login .htaccess has the same content as old .htaccess
My pages are on web hosting. I am not sure if I can restart webserver by myself.
About server log messages: any special thing except of missing of favicon.ico in folder. I repaired it.
I tuned the .htaccess file. I don't see effect for a while. Maybe after server restart?
I don´t have Coder module.
my web hosting doesn't allow me increase stack size. Is this problem always connected with some Drupal module? Is somewhere some list of Drupal modules which causes page reset after admin login? Code module isn't my case.


This problem was finally solved by Php upgrade on the side of hosting server!
Restart webserver

Might be a webserver issue. Try restarting you webserver and check if it solves your issue.

Check server logs

If that doesn't help either, check your webserver's error log to see if there is any special error message in these that helps.

Tune the .htaccess file

Modified the .htaccess file and replace the default clean URL rewrites with this:

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !=/favicon.ico
RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]


Coder module


Option a: Remove the Code module

A complete different reason for this issue is Coder makes Drupal go to "Connection was reset" browser error. So if you have the Coder module installed/enabled, then disable and uninstall it and ALSO remove that module from the module folder.
Option b (if using WAMP): increase the stack size

Be aware that preg_match_all uses the stack which may be too small. PHP crashes and then Apache crashes (and restarts). The fix is to increase the stack size to match a default Linux PHP Apache setup. To do so, increase the Apache stack size to 8MB by adding a line to the end of httpd.conf (surrounded by a IfModule mpm_winnt_module and matching /IfModule tag):


  ThreadStackSize 8388608


After restarting the webserver you can then use any version of the Coder module (and other modules which have this issue ...).

More details: https://www.drupal.org/node/1597820#comment-6094060