Error after enabling Apache module

In Webmin > Configure Apache Modules page:

I unchecked the "ruby" module and clicked on the "Enable selected modules" button (despite I did want to disable it).

Resulting page showed only:

* Starting web server apache2
(98)Address already in use: make_sock: could not bind to address 0.0.0.0:80
no listening sockets available, shutting down
Unable to open logs
...fail!

Checking with a2dismod on the shell did show the ruby module was disabled yet.

Apache was not running anymore, starting with /etc/init.d/apache start got it running again.

Status: 
Closed (fixed)