I've just upgraded from 4.5.2 to 4.7.1 and everything seemed to be working OK. I was able to use the system fine for an hour or so.
Then I was trying to re-assign some transactions from one user to another using PHPMyAdmin (by changing the contact id--I've done this before without problems) and suddenly I get a 500 Server error and nothing works.
Looking in the logs I find:
Fatal error: Call to undefined method CRM_Utils_System::isUserLoggedIn() in /var/www/vhosts//httpdocs/wp-content/plugins/civicrm/civicrm/CRM/Core/BAO/UFMatch.php on line 98
I also can see some references to:
Call to undefined method CRM_Utils_System::getUFLocale()
I can't see how a change in data can have caused this??
I re-imported the db (back to the 4.5.2 version) but I still can't access anything--I can't even run the upgrade script.
I put a clean install of the 4.7.1 plugin code and that's not fixed it either.
I'm stuck, it works fine on the test system but is totally broken on my live system now.
Update 9th Feb:
I'm running: PHP Version 5.3.25 MySQL Version: 5.5.32 Unfortunately because it's a shared hosted system, I'm not sure I can get the version of PHP updated.