I have tried enabling Web Sharing in MAC OSX 10.7.4, but after clicking to check it uncheck it self. I know there's a similar question for it, that is, Web Sharing (Apache) won't turn on in Lion.
Here is crash log that I get in "/var/log/apache2/error_log" file:
[Wed Mar 13 17:46:52 2013] [notice] Digest: generating secret for digest authentication ...
[Wed Mar 13 17:46:52 2013] [notice] Digest: done
[Wed Mar 13 17:46:52 2013] [notice] Apache/2.2.21 (Unix) DAV/2 configured -- resuming normal operations
[Wed Mar 13 17:49:51 2013] [error] [client ::1] File does not exist: /usr/htdocs
[Wed Mar 13 17:52:20 2013] [error] [client ::1] File does not exist: /usr/htdocs
[Wed Mar 13 17:52:59 2013] [notice] caught SIGTERM, shutting down
httpd: Could not reliably determine the server's fully qualified domain name, using Arpit.local for ServerName
[Mon Mar 18 18:23:03 2013] [notice] Digest: generating secret for digest authentication ...
[Mon Mar 18 18:23:03 2013] [notice] Digest: done
[Mon Mar 18 18:23:03 2013] [notice] Apache/2.2.21 (Unix) DAV/2 configured -- resuming normal operations
[Mon Mar 18 18:23:05 2013] [notice] caught SIGTERM, shutting down
httpd: Could not reliably determine the server's fully qualified domain name, using Arpit.local for ServerName
No log handling enabled - using stderr logging
Created directory: /var/db/net-snmp
Created directory: /var/db/net-snmp/mib_indexes
[Wed May 01 16:36:04 2013] [notice] Digest: generating secret for digest authentication ...
[Wed May 01 16:36:04 2013] [notice] Digest: done
[Wed May 01 16:36:04 2013] [notice] Apache/2.2.21 (Unix) DAV/2 PHP/5.3.10 with Suhosin-Patch configured -- resuming normal operations
[Wed May 01 16:43:26 2013] [notice] caught SIGTERM, shutting down
httpd: Could not reliably determine the server's fully qualified domain name, using Arpit.local for ServerName
[Wed May 01 16:43:26 2013] [notice] Digest: generating secret for digest authentication ...
[Wed May 01 16:43:26 2013] [notice] Digest: done
[Wed May 01 16:43:26 2013] [notice] Apache/2.2.21 (Unix) DAV/2 PHP/5.3.10 with Suhosin-Patch configured -- resuming normal operations
[Wed May 01 17:24:26 2013] [notice] caught SIGTERM, shutting down
I tried looking into it but couldn't get exact reason.