I am facing the same error. This is the standard Sites installer available on the Oracle.com site.
I'm using Oracle Linux 5, WLS 10.3.6.
The specified class "org.apache.commons.logging.impl.Log4JLogger" is actually in /user_projects/domains/base_domain/cs/WEB-INF/lib/commons-logging-1.1.1.jar, which is part of WebCenter Sites installation and also in /oracle_common/lib/java/shared/apache.commons.logging/1.0.3/commons-logging.jar, which is in the WLS class-path.
Is it possible that because one is in the class-path and one is deployed with the WebCenter Sites application, WLS get confused in which one it should use?
Does anybody have any hints on what might be wrong?