Incorrect sesskey submitted, form not accepted!

More information about this error

Debug info:
Error code: invalidsesskey
Stack trace:
  • line 476 of \lib\setuplib.php: moodle_exception thrown
  • line 1046 of \lib\sessionlib.php: call to print_error()
  • line 44 of \calendar\set.php: call to require_sesskey()