What is undefined symbol: pam_start

[Guest]

Can someone point me in the right direction on where to start troubleshooting the following error:

Starting apache...
Syntax error on line 56 of /etc/apache/conf/apache.conf:
Cannot load /etc/apache/extramodules/libphp4.so into server: /etc/apache/extramodules/libphp4.so: undefined symbol: pam_start

What is an undefined symbol? Is this a php error or a pam error. pam is aleady emerged into the system and I have verified by emerge search pam returns:

sys-libs/pam
Latest version Available: 0.75-r6
Latest version Installed: 0.75-r6
Homepage: http://www.redhat.com/linux-info/pam/
Description:
Pluggable Authentication Modules

Also libphp4.so is indeed located in the extramodules directory!

Thanks!