error/moodle/invalidsesskey
From MoodleDocs
Some reasons why you might have got an "Invalid Sesskey" message are:
- Your site doesn't have the PHP setting "sessions.autostart=0" (see Installing Moodle - software)
- You logged out at some time between opening the form and submitting it.
- You have followed a bad link to a form script.
- Your database has an incorrect value for sessioncookiepath in the mdl_config table.
- You edited the code in a file on the server while logged in to your moodle website.
See also
- Using Moodle incorrect sesskey - occasional failures forum discussion