Ho risolto facendo in questo modo, sono andato all'interno del mio spazio SQL e ho creato la tabella direttamente tramite comando SQL.
Ecco qual'è il codice da inserire
CREATE TABLE `#__postinstall_messages` (
`postinstall_message_id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`extension_id` bigint(20) NOT NULL DEFAULT 700 COMMENT 'FK to #__extensions',
`title_key` varchar(255) NOT NULL DEFAULT '' COMMENT 'Lang key for the title',
`description_key` varchar(255) NOT NULL DEFAULT '' COMMENT 'Lang key for description',
`action_key` varchar(255) NOT NULL DEFAULT '',
`language_extension` varchar(255) NOT NULL DEFAULT 'com_postinstall' COMMENT 'Extension holding lang keys',
`language_client_id` tinyint(3) NOT NULL DEFAULT '1',
`type` varchar(10) NOT NULL DEFAULT 'link' COMMENT 'Message type - message, link, action',
`action_file` varchar(255) DEFAULT '' COMMENT 'RAD URI to the PHP file containing action method',
`action` varchar(255) DEFAULT '' COMMENT 'Action method name or URL',
`condition_file` varchar(255) DEFAULT NULL COMMENT 'RAD URI to file holding display condition method',
`condition_method` varchar(255) DEFAULT NULL COMMENT 'Display condition method, must return boolean',
`version_introduced` varchar(50) NOT NULL DEFAULT '3.2.0' COMMENT 'Version when this message was introduced',
`enabled` tinyint(3) NOT NULL DEFAULT 1,
PRIMARY KEY (`postinstall_message_id`)
) DEFAULT CHARSET=utf8;
