Error message when restore a backup of course including serveral forumngs

1. ForumNG "Course forum - Science"

Missing parent post 615800 for 434393 (0)
/fs2/www/html/rg3598/ou-moodle/mod/forumng/restorelib.php:498
#0 /fs2/www/html/rg3598/ou-moodle/mod/forumng/restorelib.php(446):
forumng_restore_post(Object(stdClass), Array, Object(stdClass))
#1 /fs2/www/html/rg3598/ou-moodle/mod/forumng/restorelib.php(102):
forumng_restore_discussion(Object(stdClass), Array, Object(stdClass))
#2 /fs2/www/html/rg3598/ou-moodle/backup/restorelib.php(5051):
forumng_restore_mods(Object(object), Object(stdClass))
#3 /fs2/www/html/rg3598/ou-moodle/backup/restorelib.php(9875):
restore_create_modules(Object(stdClass), '/fs2/www/html/r...')
#4 /fs2/www/html/rg3598/ou-moodle/backup/restore_execute.html(77):
restore_execute(Object(stdClass), Object(stdClass), Object(stdClass), '')
#5 /fs2/www/html/rg3598/ou-moodle/backup/restore.php(193):
include_once('/fs2/www/html/r...')
#6

{main}

This restore has failed (even though it may say otherwise later). Resolve this
problem before continuing.
# [ Restore of forumng succeeded]ForumNG "Masters forum"
Warning: Missing user for post (old id) 508429, setting to admin.
# [ Restore of forumng succeeded]ForumNG "Tutor forum"
Warning: Missing delete user for post (old id) 839639, setting to admin.

Missing parent post 799013 for 627097 (0)
/fs2/www/html/rg3598/ou-moodle/mod/forumng/restorelib.php:498
#0 /fs2/www/html/rg3598/ou-moodle/mod/forumng/restorelib.php(446):
forumng_restore_post(Object(stdClass), Array, Object(stdClass))
#1 /fs2/www/html/rg3598/ou-moodle/mod/forumng/restorelib.php(102):
forumng_restore_discussion(Object(stdClass), Array, Object(stdClass))
#2 /fs2/www/html/rg3598/ou-moodle/backup/restorelib.php(5051):
forumng_restore_mods(Object(object), Object(stdClass))
#3 /fs2/www/html/rg3598/ou-moodle/backup/restorelib.php(9875):
restore_create_modules(Object(stdClass), '/fs2/www/html/r...')
#4 /fs2/www/html/rg3598/ou-moodle/backup/restore_execute.html(77):
restore_execute(Object(stdClass), Object(stdClass), Object(stdClass), '')
#5 /fs2/www/html/rg3598/ou-moodle/backup/restore.php(193):
include_once('/fs2/www/html/r...')
#6 {main}

This restore has failed (even though it may say otherwise later). Resolve this
problem before continuing.
[ Restore of forumng succeeded]