How do I mask an unconventional subdomain port

[elitemobb]

If I try to restart apache with the custom vhost configured like above I get a syntax error saying it doesnt recognize ProxyPreserveHost

Code:

service apache2 restart
Syntax error on line 95 of /etc/sentora/configs/apache/httpd-vhosts.conf:
Invalid command 'ProxyPreserveHost', perhaps misspelled or defined by a module not included in the server configuration
Action 'configtest' failed.
The Apache error log may have more information.
  ...fail!

and thats with this subdomain custom vhost configuration

Code:

Domain Enabled x
Suhosin Enabled x
OpenBase Enabled x
Port Override: 8080
Forward Port 80 to Overriden Port:    X
Custom Entry:
ProxyPreserveHost On

  # setup the proxy
  <Proxy *>
      Order allow,deny
      Allow from all
  </Proxy>
  ProxyPass / http://sub.domain.com:8080/
  ProxyPassReverse / http://sub.domain.com:8080/