If we continuously receive errors in our Moodle it is best to activate the debugging mode and thus be able to identify the problems
One way is to activate the maintenance mode first and then go to Site Administration -> Development -> Debugging, then in the drop-down list select "Developer"
Another way is by directly editing the config.php file and placing the following code at the beginning:
@error_reporting (E_ALL | E_STRICT);
@ini_set ('display_errors', '1');
$ CFG-> debug = (E_ALL | E_STRICT);
$ CFG-> debugdisplay = 1;