i had this error -
i installed ispconfig 3 on centos, but then my proftpd was not working, so i remove ispconfig3 and installed ispconfig 2, then after apache could not be started i would get this error:

# /etc/init.d/httpd restart
Stopping httpd: [FAILED]
Starting httpd: Warning: DocumentRoot [/usr/local/ispconfig/interface/web/] does not exist


after troubleshooting, this is what i found out.

open the apache configuration file:
SHELL COMMAND:
nano /etc/httpd/conf/httpd.conf


hit Control+w

ENTER:
sites-enabled


and comment out the line, so make it look like this:

NameVirtualHost *:80
NameVirtualHost *:443
#Include /etc/httpd/conf/sites-enabled/


so now try starting apache again.

SHELL COMMAND:
/etc/init.d/httpd start



now it should work

------------------------------------- notes -----------------

[root@jpst vhosts]# /etc/init.d/httpd restart
Stopping httpd: [FAILED]
Starting httpd: httpd: Syntax error on line 1047 of /etc/httpd/conf/httpd.conf: Could not open configuration file /etc/httpd/conf/vhosts/Vhosts_ispconfig.conf: No such file or directory

this is how i was able to find what the problem was