I'm having the same problem, running debian 3.1 64 bit with ispconfig 2.2.7
The changes is not saved anymore in Vhosts_ispconfig.conf and if I clean the file of it's content, and run /root/ispconfig/php/php /root/ispconfig/scripts/writeconf.php nothing is saved either.
No error message appears, but only:
and httpd -t gives Syntax OK
Help very much apriciated