Hello Heather,
Please bear in mind that you are not the only client I am responding to. On a good day I am replying to at least 10 different people. Yesterday I was actually responding to over 30 people and I had to deal with some release issues. I honestly didn't recall me replying to your earlier ticket. Sorry about the confusion.
I can give you more information about your issue so you understand the context of my reply and tell you what we can do to further troubleshoot your issue.
The class F0FUtilsCacheCleaner referenced in the error message is part of our FOF 2.x framework which we have not used since June 2016. It's not something that can come from installing an up to date version of Admin Tools – your ticket says you're trying to install the latest version, 5.7.3.
The error message in itself only gives a limited amount of information, namely that an obsolete class we haven't used since 2016 is used. Missing additional information I have to guess where it comes from. It can be either a really old version of one of our extensions installed on your site or a third party extension. FOF is our framework but it's open source. It can and has been used by other developers, unaffiliated with us.
My first guess in the context of replying to a ticket about installing the latest version of Admin Tools is that probably an at least 5 year old version of Admin Tools would be in play. Since you said you have already deleted these folders this is now a remote possibility but not one I can rule out. These old versions of Admin Tools included other system plugins which might have been referencing that class. There's only one way to find out what is really going on.
Edit your site's configuration.php file and find the following two lines (they will probably not be one directly under the other):
public $debug = '0';
public $error_reporting = 'none';
Change them so they read
public $debug = '1';
public $error_reporting = 'development';
This raises the error reporting to the maximum level which will give us more information.
Try to access your site again. Below the error message there will be much more information which tells us exactly where this error comes from. Please print that page as a PDF, put the PDF in a ZIP file and attach it to your next reply. It will give me the information I need to help you better.
Also, in the last ticket I told you that the PHP on your server was doing weird things, like claiming a writable file with the correct permissions was not accessible. Have you addressed this issue? If not, any further steps we take will most definitely be for naught. That's a fundamental problem. At the very least check that the FTP layer in Global Configuration is disabled.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!