Error while renewing Let's Encrypt

Hi everyone!

I get the following error, when I’m trying to renew my Let’s Encrypt certificate.

Cert is due for renewal, auto-renewing...
Could not choose appropriate plugin: The apache plugin is not working; there may be problems with your existing configuration.
The error was: PluginError(('There has been an error in parsing the file (%s): %s', u'/etc/apache2/sites-available/letsencrypt.log', u'Syntax error'),)
Attempting to renew cert from /etc/letsencrypt/renewal/probiz.at.conf produced an unexpected error: The apache plugin is not working; there may be problems with your existing configuration.
The error was: PluginError(('There has been an error in parsing the file (%s): %s', u'/etc/apache2/sites-available/letsencrypt.log', u'Syntax error'),). Skipping.

All renewal attempts failed. The following certs could not be renewed:
  /etc/letsencrypt/live/probiz.at/fullchain.pem (failure)
1 renew failure(s), 0 parse failure(s)

I’ve been reading all kinds of tutorials and comments here in this forum - but I’m thoroughly stuck.

My /sites-available folder has

probiz.at-ssl.conf  letsencrypt.log  pro-biz.at.conf  app.probiz.at.conf  app.probiz.at-ssl.conf  .  probiz.at.conf  default-ssl.conf  000-default.conf

in it. probiz.at-ssl-conf has the following content:

### New SSL Config for probiz.at ###
<VirtualHost IP_OF_DROPLET:443>
        ServerAdmin PERSONAL E-MAIL ADDRESS
        ServerName probiz.at
        ServerAlias www.probiz.at
        DocumentRoot /var/www/html

        <Directory /var/www/html/>
            Options Indexes FollowSymLinks
            AllowOverride All
            Require all granted
        </Directory>

        SSLEngine ON
        Include /etc/letsencrypt/options-ssl-apache.conf
        SSLCertificateFile /etc/letsencrypt/live/probiz.at/cert.pem
        SSLCertificateKeyFile /etc/letsencrypt/live/probiz.at/privkey.pem
        SSLCertificateChainFile /etc/letsencrypt/live/probiz.at/fullchain.pem

        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

What am I missing here? Thanks for your help!