Update was from 2.3.3 Eng up to 2.7.
Did everything as usual: backup DB & files, turning off plugins, then wp-admin/upgrade.php. There were no any problems during update process, and later blog was working OK.
But after testing it surfaced that after doing some changes you can end up on white screen. Either all changes are saved. The same with comments. After Update nothing was set up above the existing configuration - no plug-ins, nothing at all. After log out i can't reach admin panel, white screen all the time. But blog itself is working.
Does anyone know what can be the problem and how can it be fixed?
problem is not in RAM memory, blog is located on a dedicated server.