Joomla! Documentation™

The most common errors from Joomla 3.10 to 4 can be summed up in two items:

• Technical Specifications not met
• Third-party extension incompatibility

Go through your extensions in the Manage tab again. Likely, there is something in there that you missed. Have someone else look for you if you must. Sometimes it just takes another set of eyes to find extensions that need to be uninstalled or updated before a successful migration happens.

This document is a work in progress. You may add errors and solutions to this page. In the meantime, if you have an error from 3.10 to 4.x, copy the error into a Google search bar eliminating the parts that are server/site specific.

For example, if you get an error that says:

Fatal error: Call to a member function get() on a non-object in home/account/public_html/directory/administrator/components/com_installer/controller.php on line 39

Cut out the home/account/public_html/directory portion of the error during your search so you get better results.

Errors & Solutions

Add errors and solutions below. Note if you have never added a link to a document before, save your text before linking! Then once saved go back in and add the link.

isClient and isAdmin Errors

These errors shows that you have third-party extensions using isClient or isAdmin which are no longer in use. You must assess and uninstall or disable/unpublish all third-third party extensions that are not compatible with Joomla 4.x. You can disable these extensions whilst seeing this error by disabling them in the database to get control back.

Blank Screen

1. Check the page source. If it looks like the complete HTML code is there, you may have a JavaScript error. If there is no code at all, it is a PHP error.
2. Check logs/joomla_update.php to see if a proper update happened. Include this log with any post to the Joomla Forums so that people can help you. If the site is updated properly, you can use phpMyAdmin to disable third-party plugins that you may have overlooked before updating to Joomla! 4.x.

SELECT * FROM `#__extensions` where type = 'plugin' and extension_id > 700
Use your own prefix (#_)

Set enabled column to 0 to disable the plugin.

You need to restore from a backup if logs/joomla_update.php is incomplete.

Alternative Ways to Get to the Database and Discover tabs

Discover URL: index.php?option=com_installer&view=discover

Database URL: index.php?option=com_installer&view=database