Make sure that PHP extension "curl" is turned on. Also make sure that PHP parameter "disable_functions" doesn't include function "shell_exec". If it is included then delete it from there and restart server.
Site.pro provides plugin for ISPmanager 5. Site.pro does not provide/support plugin for ISPmanager4.
Try to delete FTP account(s) with username of format "s12abc34" on your ISPmanager account. After that open builder from ISPmanager again and try to publish website.