error/Unable to find discussion with id

More information about this error

Debug info:
Error code: Unable to find discussion with id
$a contents:
Stack trace:
  • line 48 of /mod/forum/discuss.php: moodle_exception thrown
Output buffer: <br /> <b>Notice</b>: Undefined variable: discussionid in <b>/var/www/html/mod/forum/discuss.php</b> on line <b>48</b><br />