Move site to another server and change domain name

Hello All,

We are developing a RT site. We started on a dev server using a dev URL

I then used Cpanel copy to copy the account over to the live server, and changed the site URL in the wp_options table in the database.

I am now getting the following errors.

Warning: session_start(): open(/tmp/sess_f0c4831ea5b2c2af36216797a9546961, O_RDWR) failed: Permission denied (13) in /home/%%%%%%/public_html/wp-content/themes/RT/framework/_config.php on line 70

Warning: session_start(): Cannot send session cache limiter – headers already sent (output started at /home/%%%%%%/public_html/wp-content/themes/RT/framework/_config.php:70) in /home/%%%%%%/public_html/wp-content/themes/RT/framework/_config.php on line 70

Warning: Unknown: open(/tmp/sess_f0c4831ea5b2c2af36216797a9546961, O_RDWR) failed: Permission denied (13) in Unknown on line 0

Any ideas why? What do I need to set, clear or change where to get this working on the live server?

Cheers