phplist on Ubuntu 16.04.1 server - Initialise the Database no reaction : I got a new server with Ubuntu 16.04.1 installed. It comes with php7
I installed phplist-3.2.5 in the root of the host pr.xxx.com

I tried in the config file:
$pageroot = '/';   and
$pageroot = '';

http://pr.xxx.com/admin let me fill out the PhpList initialisation, but the button [Continue] does not show me any reaction. 

No log file (syslog, apache error) gives me a clue.

login to the mysql shows that the table has not been created either.


Maybe related: On the right side I get the information:
Error on line 66 of /var/www/pr.xxx.com/admin/ui/dressprow/onyx-rss.php: PHP's XML Extension is not loaded or available.

How can I track down this problem?