Fatal error: Call to undefined method modX::isFrontend()

When you upgrade MODx there are chances that you will see error something like this

What’s the Problem ?

This simply means “isFrontend()” method is deprecated, and is no more supported.

Who is causing problem ?

Take a look at the file in error “4.include.cache.php” and notice the “4”. This is nothing but ID of plugin which is using this method and causing problem.

Solution ?

1) Go to MySQL -> find table “modx_site_plugins” and then find plugin name with id 4
2) Now go to Manager -> System -> Plugin Management and upgrade that plugin to latest version OR if upgrade option isnt there then update “disabled” column and set it to “1”.

Now try re-logging to manager and everything will be fine.

Note : If needed clear the cache ( It worked for me without clearing cache, so i guess its its not mandatory step.)