Error enabling MPM Worker

Solution 1:

You need to install 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.

and make sure that this extension exists in /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