Failed to start apache

Since upgrading from Ubuntu 12.04 to 14.04.2, I recive the following error when attempting to start apache2:

Failed to start apache :

• Starting web server apache2
• The apache2 configtest failed. Output of config test was: AH00526: Syntax error on line 57 of /etc/apache2/apache2.conf: Invalid command 'LockFile', perhaps misspelled or defined by a module not included in the server configuration Action 'configtest' failed. The Apache error log may have more information.

As a temporary fix, I commented out the line

LockFile /var/lock/apache2/accept.lock

and replaced it with

Mutex file:${APACHE_LOCK_DIR} default

and added the folder /run/lock/apache2/ssl_mutex

However, I ran updates and the problem reoccurred. Any sugestions?