Plesk 7.5.4: Error: HTTPD_INCLUDE_D not defined

Normally, this error will pop up when you attempt to restart a Plesk-related service, like httpsd, psa-spamassassin or qmail:

Error: HTTPD_INCLUDE_D not defined

This basically means that Plesk is unable to get some required configuration directives from the /etc/psa/psa.conf file. If you can’t find the directive in the file that Plesk is complaining about, check your Plesk RPM’s with rpm:

# rpm -q psa

Most likely, you will find that there is a psa-7.5.4 RPM and a psa-8.1.0 or psa-8.1.1 RPM installed simultaneously. This generally appears because of a botched upgrade that was started within Plesk by the admin user.

To fix the issue, get the psa-7.5.4 RPM from autoinstall.plesk.com. Remove the psa-8.1.1 RPM and install the psa-7.5.4 RPM again rather forcefully:

# rpm -ev psa-8.1.1...
# rpm -Uvh --force --nodeps psa-7.5.4...
# /etc/init.d/psa restart

At this point, you can download the command line autoinstaller and try the Plesk upgrade again.

Further reading: http://forum.swsoft.com/showthread.php?threadid=32299