We are having the same error(500 Internal Server Error) when calling domain.com/cpanel, /webmail etc.
We tried to increase the Timeout value in "/usr/local/lsws/conf/httpd_config.xml" but no luck. Also we checked error_log in "/usr/local/apache/logs" and got the following in it.
2013-02-24 04:46:04.611 [NOTICE] [208.x.x.x:33290-0#APVH_domain.com] Premature end of response header.
2013-02-24 04:48:16.595 [NOTICE] [208.x.x.x:33290-0#APVH_domain.com] Premature end of response header.
Nothing generates on stderr.log. This is working fine when switching from litespeed to apache. Please help!!!