Port 443 goes active, https causes error

[rsthomas]

this problem is caused on CentOS installs by a duplicate Listen 443 statement in /etc/httpd/conf.d/ssl.conf 

Thanks for the tip. I am running on Ubunto 14.04, which does not have a /etc/httpd/conf.d/ssl.conf file. However, I did a find for ssl.conf. Of the nine files returned, this is the only one which references port 443:

/opt/eff.org/certbot/venv/lib/python2.7/site-packages/certbot_apache/tests/testdata/centos7_apache/apache/httpd/conf.d/ssl.conf

Reference:
# When we also provide SSL we have to listen to the
# the HTTPS port in addition.
#
Listen 443 https

I don't know if this has anything to do with the issue because I am running on Unbuntu and not Centos. Even if it does, I don't know what to do about it other than rem out the Listen 443 https line.

Could all this have something to do with Let's Encrypt?

If interested, this is the link to a portion of my httpd-vhosts.conf file which shows the SSL setting for the Sentora control panel as well as two domains that had been configured with SSL -- http://rstunlimited.com/httpd-vhosts.pdf.