Apache modules mod_security (mod_security2) and mod_evasive20 and PHP extension Suhosin on the publishing server may have various negative effects on the workings of Parallels Plesk Sitebuilder. Among them is the inability to manage modules or site publishing.
mod_security (mod_security2), mod_evasive20, and Suhosin were not thoroughly tested with Plesk Sitebuilder. It is recommended to disable them on the publishing server.
To leave mod_seturity enabled you may try adding the directives below to the mod_security configuration.
<Directory /path/to/your-domain.com/public_html> <Files server.php> SecFilterScanPOST Off </Files> </Directory>
(where /path/to/your-domain.com/public_html is the location of the Apache virtual host the site is published to.)
Refer to this article for possible reasons for the error "Error! Operation has not been completed."