This is basically caused by upgrading PHPto a new version like 5.4 when you had 5.2 before and an old version of Joomla. The only solution is to upgrade Joomla or downgrade PHP, both of which can be a pain.
Strict Standards: Non-static method JLoader::import() should not be called statically in /home/userdir/public_html/libraries/joomla/import.php on line 29
Strict Standards: Non-static method JLoader::register() should not be ca........
This may sound silly but there will be conflicts/issues with the default Centos repository so you have to use a third party like remi (I prefer not to do this but it's the only option unless you migrate your sites/data to another server or can stand some downtime-not an option IMHOon a production server).
You may need to upgrade to PHP5.3 to run Joomla or many other reasons.
Your host needs to use PHP 5.2.4 or higher to run this version of Jo........
JFolder::create: Could not create directory
Plugin Install: Failed to create directory:
This can occur when trying to upload content or when installing themes/templates.
It's usually not a permissions issue per say but doing a 777 (which is very insecure) will fix it. But the real problem solution is that the owner of the files is different than the owner of the Apache process/server.
Eg. if your Apache is running as user "apache........