“Ajax Loading Error: Category not found” Error when Updating a Joomla Website

A new client, with a Joomla 3.6.0 website, called us yesterday evening and told us that every time he tries to update his Joomla website, he sees the following the following error:

Ajax Loading Error: Category not found

So, we went to his website, and tried to update Joomla, but, as expected, we saw the above error, in a JavaScript popup. Hmmm! Debugging these JavaScript problems is typically not easy, we thought… But we promised the client that we will find a solution for him!

So, the first thing that was on our mind was cache: we disabled all types of cache on the website (global cache and system cache), and then we cleared the cache (Joomla cache and browser cache), and then we tried to update the website again, but we still saw the above error.

We searched for the error in the Joomla code base, in hope of finding the exact location of the problem, but we couldn’t find anything. To be honest, it’s not that we didn’t find anything, we did find something, but what we found wasn’t really helpful in getting to the root of the problem. So we decided to stop beating around the bushes, and instead, we took an approach that was completely against our programming habits: debugging Ajax code (nobody likes to debug Ajax code).

So we opened the JavaScript file containing the Ajax code responsible for throwing that error, which is the update.js file (which is located under the media/com_joomlaupdate/js folder) and we checked its code. After a thorough examination, we knew that for us to know what is really going on, we needed to find which PHP file is processing the Ajax request. And so we changed the following line in the update.js file:

var message = 'AJAX Loading Error: ' + req.statusText;

to this line:

var message = 'AJAX Loading Error: ' + req.statusText + ' update URL is: ' +  joomlaupdate_ajax_url;

We then cleared our browser cache (again), and tried to update the website, and this time, the JavaScript alert window displayed the URL that the Ajax request was being sent to. It was this one: http://www.[ourclientjoomlawebsite].com/administrator/components/com_joomlaupdate/restore.php

So, we visited the URL directly, and it had the following error:

404 – Category not found

That was odd, because the file restore.php existed. So we added the following code to the very beginning of the restore.php file (just after the opening tags):

die('In restore.php file');

We then visited the above URL again, but we were surprised to see the same error again. This meant 2 things: either there is an .htaccess rule whitelisting specific PHP files, or the file permissions/ownership were wrong. So we first checked the .htaccess file and we noticed that it had the following code in its very beginning (probably copied from here):

<Files *.php>
	Deny from all
</Files>
<Files index.php>
	Allow from all
</Files>

The above code secures the Joomla website by allowing direct access to the just one file, which is the index.php file. On the flip side, it doesn’t allow direct access to the restore.php file, which is a legitimate file used for the update.

So, we updated the above code to the following to allow access to the restore.php file…

<Files *.php>
	Deny from all
</Files>
<Files index.php>
	Allow from all
</Files>
<Files restore.php>
	Allow from all
</Files>

… and then we visited the website, but still, we saw the same error. So we quickly checked the permissions/ownership on that file and we noticed that both the permissions and the ownership were incorrect: the permissions were set to 600 (note that we didn’t notice this when editing the file because we edited the file while ssh’ing as root), and the ownership was set to root. We suspect that that file was infected previously and so whoever did the cleanup decided to just make the file completely inaccessible (with the exception for the root user) after the cleanup process. So we changed the file permissions to 444 and we changed the ownership and the group ownership to the cPanel user of the website. We then visited the file, and this time, we saw the message that we added in the restore.php file. We then removed the die statement that we have added, and we tried updating the website, and, as expected, it worked smoothly! Hurray! Lush homes all around! (In case you’re wondering, that Lush homes thing is from the game Tales of Monkey Island).

So, if you, our dear reader, are seeing the Ajax Loading Error: Category not found popup when trying to update your website, then fear not: check if your .htaccess file is allowing access to only specific files and also check the ownership/permissions on the restore.php file. If everything checks and you are still having the problem, then it’s time to contact the Joomla experts! We are there for you 24/7/365, we know our Joomla, and our fees are super affordable!