Warning: session_start();

I have a problem that literally happened overnight. One day it was working, and the next, it wasn't. My php script, which is in a subdomain now outputs the error "Warning: session_start() [function.session-start]: open(/var/www/vhosts/sur/sur.com/httpdocs/subdomains/ns/phptmpdir/sess_71c80badeda0a257401e03c36ffbb423, O_RDWR) failed: Permission denied (13) in /var/www/vhosts/sur/sur.com/httpdocs/subdomains/ns/includes/header.php on line 3

and then in the footer
Warning: Unknown: open(/var/www/vhosts/sur/sur.com/httpdocs/subdomains/ns/phptmpdir/sess_71c80badeda0a257401e03c36ffbb423, O_RDWR) failed: Permission denied (13) in Unknown on line 0

Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/www/vhosts/sur/sur.com/httpdocs/subdomains/ns/phptmpdir) in Unknown on line 0

I googled this and people said to change the session directory. When I looked at that, all I saw was N/path or something like that in the php.ini. Any help? i need to get this solved

Thanks

most probably, your permissions has changed somehow.
to fix that,
in console:
chmod a+w -Rf /var/www/vhosts/sur/sur.com/httpdocs/subdomains/ns/phptmpdir

Thanks for the reply. I saw the file permission earlier, its 777. I tried what you gave me and I still get the error. Any more ideas? I need to get this solved soon :/

I use EHCP =)

Even the tmp file is 777

I use EHCP =)