Doing Joomla! upgrades are not always the easiest and quickest things to do. Especially when you have to upgrade for few versions at once. You can encounter different issues, like messed up file systems, missing libraries, corrupted or outdated template overrides, old and abandoned extensions, etc.
Recently while doing upgrades I encountered a strange error when trying to load the article list view in the backend:
I was presented with this error:
Fatal error: 500 Layout default_batch not found. . I did the usual debugging procedures, but since I didn’t have access to the server logs it was difficult. Luckily, by switching on the debugging in the config, I was presented with the exact place where this error exception was thrown. By adding some “old-school” var_dump()’s I was able to figure out that the Joomla! installation was missing some important core files.
What I did was I went to Components > Joomla Update and clicked on the “Check for updates” button:
and I was presented with the following window:
By clicking on the “Reinstall Joomla core files” button all of the core files were re-downloaded and replaced. After that, the error was gone, and the article list showed properly.
Bonus tip: You may also want to check the Administrator template, like “Isis” for outdated or corrupted template overrides in its “HTML” folder.