Hi there,

I appreciate you reaching out. I sincerely apologize for this oversight. I am not able to login administrator area. Can you help me?

-Thanks

I can't do that anymore either. What does this error mean exactly?

Thank you

Hi Dominik,

Probably one of installed extension made that mess. It could be extra installed by you plugin, this is common reason. Or Joomla installation was damaged by extra files.

Anyway to see more than a single error message:

1. Use FTP Tool
2. Open configuration.php file in edit mode
3. Turn on debug mode
4. And showing errors rename from "default" to maximum

Video guide for Joomla Beginners >> https://youtu.be/0W6ZqrbbkbU?feature=shared&t=155

Also check error logs in cPanel.

I hope you have website backup (or hosting company has)

BTW

On forum.joomla.org I also found that suggestion (it doesn't have to be true in your case)

This is error is thrown by a corrupted J! website. It it is possible that you have parts of J! 4.x in your website left over from failed attempts to update from J! 3.10 to J! 4.x that you need to cleanse. I suggest that you try to restore your J! 3.10.11 website properly: https://forum.joomla.org/viewtopic.php?f=812&t=995470#p3667508