Você precisa instalar o php-zts
package:
Name : php-zts
Version : 5.3.8
Release : 2.el5.art
Architecture: x86_64
Size : 4210728
Packager : None
Group : Development/Languages
URL : http://www.php.net/
Repository : atomic
Summary : Thread-safe PHP interpreter for use with the Apache HTTP Server
Description :
The php-zts package contains a module for use with the Apache HTTP
Server which can operate under a threaded server processing model.
e verifique se essa extensão existe em /etc/httpd/modules
:
ls -l /etc/httpd/modules/libphp5-zts.so
-rwxr-xr-x 1 root root 4210728 Nov 1 05:29 /etc/httpd/modules/libphp5-zts.so