@hsm-berlin Could you switch on debug in the global configuration so you can see the complete call stack and report it back? Thanks in advance.

@richard67 I will try it, but this is my production website and the error was not generated by myself. But I check the access-log.

Since when do you get these errors? Have they started to appear after an update? We need more information.

At a first look it seems there has an extension not been uninstalled properly, so assets (i.e. access rules) were remaining for which no extension exists anymore.

@hsm-berlin Could you test and report back if the changes here solve your issue? https://github.com/joomla/joomla-cms/pull/36786/files

Of course make a backup of the original PHP file before you modify it or replace it by the modified version from my PR, so you can later revert it if necessary.

Thanks in advance.

O.K. I was able to find the link that caused the error. It was a menu entry to an article. The link was missing the .html. After I called the link with .html for the first time, the error was no longer displayed. Therefore, unfortunately, I can no longer test it. If I find the error again, I will test the new code.

@hsm-berlin You always do all works on the life site, not have a copy on a subdomain there for testing or on a local computer with a webserver? That's very courageous. Do you do at least backups of files and database (with or without the help of well known useful products) before updating the CMS or extensions or installing questionable extensions? If not: Would you mind if we call you "danger seeker"? ?

@richard67 I have a test-system on a local server, but that did not produce this error. So what should I do? O course I make daily backups. ;-) Thanks for your work!

Anyway, closing as having a pull request of which I am convinced it will solve it if it can be reproduced again, see #36786 . Thanks for reporting.