PHP: Call to undefined function session_start()

Hi! I installed php5 and php5-cgi from opkg. Everything works well on the website except that error:
Call to undefined function session_start()

I definitely need _SESSION because of Error handling and so on. How can I get this fixed?

http://forum.arduino.cc/index.php?topic=247021.msg1765903#msg1765903

I tried installing php5-mod-session, but all I get is:

root@Arduino:~# opkg install php5-mod-session
Unknown package 'php5-mod-session'.
Collected errors:

  • opkg_install_cmd: Cannot install package php5-mod-session.

Any idea?

EDIT:
Sorry everything worked. Seemed that opkg update had an problem when updating (Signature check), but it worked now.

Thanks for your help!