There was a 500 error, and why only in the admin panel?

Question

PHP

Error log:

[Wed Oct 05 09:25:23 2016] [error] [client 180.76.15.12] PHP Notice:  Use of undefined constant php - assumed 'php' in /var/www-forum/templates/protostar/index.php on line 145
[Wed Oct 05 09:26:02 2016] [error] [client 213.176.242.160] PHP Notice:  Trying to get property of non-object in /var/www/includes/router.php on line 389
[Wed Oct 05 09:26:05 2016] [error] [client 213.176.242.160] PHP Notice:  Undefined index: 201 in /var/www/modules/mod_roknavmenu/lib/librokmenu/AbstractRokMenuProvider.php on line 142
[Wed Oct 05 09:26:05 2016] [error] [client 213.176.242.160] PHP Notice:  Undefined index: parent_id in /var/www/modules/mod_roknavmenu/lib/librokmenu/AbstractRokMenuProvider.php on line 143
[Wed Oct 05 09:26:44 2016] [error] [client 213.176.242.160] PHP Notice:  Trying to get property of non-object in /var/www/includes/router.php on line 389
[Wed Oct 05 09:26:49 2016] [error] [client 213.176.242.160] PHP Notice:  Trying to get property of non-object in /var/www/includes/router.php on line 389
[Wed Oct 05 09:32:21 2016] [error] [client 213.176.242.160] PHP Notice:  Trying to get property of non-object in /var/www/includes/router.php on line 389

The strangest thing is that this error appeared for no reason yesterday, on 2 sites at once (on different servers and CMS, Joomla and Modx), before that everything was fine, the only thing that is updated on the site is the content. The error appears only in the admin panel and when adding files to the material, or when you close any material, and every other time. What could be the problem? This could not have appeared out of the blue, on the same day, on two different sites.

Answer 1

500I in 99% of cases occurs due to some kind of fatal error

Answer 2

The most common cause of error 500 (Internal Server Error, internal server error) is the incorrect syntax of the .htaccess file or the presence of unsupported directives in it. Most often, it is enough to comment out the Options directive (to do this, put a hash mark at the beginning of the line - #), and the problem will disappear.
Error 500 can also be caused by mishandling CGI scripts:
CGI scripts must have UNIX (\n) line endings, not Windows (\r\n) line endings. To do this, they must be uploaded to the server via FTP in ASCII mode.
CGI scripts and folders in which they are located must be writable only by the owner, that is, they must have the rights 0755 (drwxr-xr-x).
As a result of the CGI script, incorrect HTTP response headers were generated. In this case, to solve the problem, it is useful to refer to the error_log (it can be found in the control panel in the "Hosting / Statistics / Log files / Errors" section).

Answer 3

Either configs are broken, or .htaccess. And this may be the case if the sites on the account are infected.