No Installation Script - akeeba/onthos GitHub Wiki

The extension's XML manifest declares an installation script, but the script file is no longer present on your site. This could cause fairly minor problems when uninstalling the extension, e.g. leaving leftover database entries or installed extensions.

Why is it a problem?

Some extensions need to perform more complicated actions when they are installed, updated or uninstalled. For example, they may have to remove obsolete code files on update, install content types on installation (and remove them on uninstallation), set licensing information to the update site database record etc.

This is all done using an “installation script” which is a PHP file declaring “hook” methods which get called depending on the installation action (regular installation, discover & install, update, uninstallation). The existence of this file is declared in the extension's XML manifest file.

This issue is shown when the XML manifest shows that an installation script is supposed to exist for this extension but none can be found on your site. This may cause update or uninstallation issues which can range from mildly annoying (files or database tables left behind after uninstallation) to major (update or uninstallation fails).

Suggested fix

You will need to reinstall the extension to make sure the missing files are installed back into your site.

It is recommended that you install the package which contains the extension twice in a row, without uninstalling it before or in between.