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I believe that the problem is not in the installation no...
By what the error says, it is already installed and at start time it is giving an error in the file /etc/apache2/sites-enabled/000-default.conf.
The description of the error says that the tag is not closed (Open the file and take a look. To close the tag <VirtualHost>
use </VirtualHost>
Another thing, something nice to ask next to the question is the version of linux you are using and which is the specific distro and also show us the way you are installing apache2.
Is there a bug in the file /etc/apach2/apache2.conf, could you post it for us to look at? you even modified it?
– Felipe Gabriel