Did you remember to make the first column something unique in your call to get_records? Duplicate value '11' found in column 'id'.
line 741 of lib/dmllib.php: call to debugging()
line 945 of lib/dmllib.php: call to recordset_to_array()
line 4462 of mod/forum/lib.php: call to get_records_sql()
line 4364 of mod/forum/lib.php: call to forum_remove_user_subscriptions()
line 3019 of lib/accesslib.php: call to forum_role_unassign()
line 253 of admin/roles/assign.php: call to role_unassign()