Thank you for responding.
Sorry for the confusion:
0.0.0.0 was just an example.
The error, in German, will appear not only for all IPs. But also for pressing the save button with any changes at all. Also, the error pops up when I try and access any of the other tabs:
Web, EMail, FTP, DNS, Functions, Other.
A loose translation is:
Field: Only following signs are permitted domain: a-z A-Z 0-9 -
It's is my guess that this error is just a default and in fact there is something else wrong with my installation.
Clearly, it is something I did wrong on the initial installation and unfortunately did not "clean up" when I did a reinstallation. Here is what I did when I reinstalled:
Deleted the install_ispconfig directory.
Deleted the directories /root/ispconfig and /home/admispconfig.
Deleted the mysql database (/var/lib/mysql/db_ispconfig).
Cleaned up httpd.conf/
Anything else you can think of?