The code may lead you to believe you have an incompatible template but if you are not trying to use an old template currently that is not the issue. I actually deleted all 3.x style templates to make sure.
What the issue is, is old plugins that are not compatible but Vbulletin does not seem to account for this except that you'll see a fatal PHPerror. You should disable all plugins and then enable one by one until you find the one that is causing the issue.
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sudo mkdir -p /etc/X11/xorg.conf.d/
sudo vi /etc/X11/xorg.conf.d/20-intel.conf
On newer Ubuntu / Mint / Debian systems the file would go in: /usr/share/X11/xorg.conf.d/20-intel.conf
Type "i" and enter the following:
Section "Device"
Identifier "Intel Graphics"
Driver&n........
This happened after a customer migrated their hosting and the issue was being unable to access PHP sessions.
Warning: session_start(): open(/var/lib/php/session/sess_3e0oms763m6mrqekdnnmodlhs3, O_RDWR) failed: Permission denied (13) in /register.php(202) : eval()'d code on line 1
Solution:(use the correct ownership/permissions)
chown apache.apache -R /var/lib/php........
Login as Admin
Languages & Phrases -> Search in Phrases
Choose "Phrase Variable Name Only"
Search for: welcomemail
Edit the "Translation" box with what you'd like in it.........
[function.vB-Registry-include]: failed to open stream: No such file or directory in /www/vhosts/site.com/forums/includes/class_core.php on line 2394
This happens on a new vBulletin install where you haven't created the config.php file. Simply copy the config.php.new file into config.php and you'll be good to go.........