Symptoms

Apache fails with the following error in ~httpd2/logs/error_log :
 [emerg] (22)Invalid argument: couldn't grab the accept mutex
 [emerg] (22)Invalid argument: couldn't grab the accept mutex
 [emerg] (22)Invalid argument: couldn't grab the accept mutex
 [emerg] (22)Invalid argument: couldn't grab the accept mutex

Resolution

1.change the directive in the following files:
/hsphere/shared/apache2/conf/httpd.conf
/hsphere/shared/apache2/conf/httpd.conf.tmpl.custom

From:
AcceptMutex Default
to:
AcceptMutex flock

2. restart httpd service:
/etc/init.d/httpd stop
sleep 10
/etc/init.d/httpd start