So I guess I found the problem. I have updated my Lucid 10.04 Ubuntu server with PHP 5.4.20 and MySQL 5.5 by using launchpad repositories which installed a new libmysqlclient18.
So after trying to install a new myodbc for my Ubuntu 10.04 (with possible support for libmysqlclient18 or so?) I...
I have checked all possible log files
/opt/psa/admin/logs/httpsd_access_log
ip.add.re.ss - - [16/Oct/2013:10:00:01 +0200] "GET /admin/customer/create HTTP/1.1" 502 166 "https://server:8443/admin/customer/list?context=customers" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:24.0)...