We found the reason for the first issue with the path, it is a bug in ispconfig versions before 3.0.5 which inserted a wrong path, the problem was not visible till now as the ispconfig interface had a mod_php fall back which has been removed now for security reasons.
The second issue is most likely related to the first one, php-fcgi has a problem to connect to mysql.
Here the steps for a short fix:
Edit the file ispconfig vhost file:
Debian / Ubuntu: /etc/apache2/sites-enabled/000-ispconfig.vhsot
and change the lines:
# <IfModule mod_php5.c>
# DocumentRoot /usr/local/ispconfig/interface/web/
# AddType application/x-httpd-php .php
# <Directory /usr/local/ispconfig/interface/web>
# # php_admin_value open_basedir "/usr/local/ispconfig/interface:/usr/share:/tmp"
# Options FollowSymLinks
# AllowOverride None
# Order allow,deny
# Allow from all
# php_value magic_quotes_gpc 0
AddType application/x-httpd-php .php
# php_admin_value open_basedir "/usr/local/ispconfig/interface:/usr/share:/tmp"
Allow from all
php_value magic_quotes_gpc 0
chmod 660 /usr/local/ispconfig/interface/lib/config.inc.php
and restart apache. Then try to login again.