Question "Invalid argument" warning given after 1.6.0 to 1.6.1 upgrade

Database collation check: The collation of your table fields are correct

Legacy mode: Enabled | Joomla! SEF: Enabled | Joomla! SEF rewrite: Enabled | FTP layer: Disabled |

This message contains confidential information

htaccess: Exists | PHP environment: Max execution time: 30 seconds | Max execution memory: 128M | Max file upload: 20M

Joomla default template details : yoo_blueprint | author: YOOtheme | version: 1.5.0 | creationdate: September 2008

Kunena version detailled: Installed version: 1.6.1 | Build: 3858 | Version name: Timu | Kunena detailled configuration:

Warning: Spoiler!

[th]Kunena config settings:[/th]

board_title	ReGroup Forum
board_offline	0
board_ofset	0
offline_message	<h2>The Forum is currently offline for maintenance.</h2> Check back soon!
enablerss	1
enablepdf	1
threads_per_page	20
messages_per_page	6
messages_per_page_search	15
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template	default
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catimagepath	category_images/
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rteheight	300
enableforumjump	1
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username	1
askemail	0
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showkarma	1
useredit	1
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useredittimegrace	600
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allowsubscriptions	1
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maxsubject	50
maxsig	300
regonly	0
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pubwrite	0
floodprotection	0
mailmod	0
mailadmin	1
captcha	1
mailfull	1
allowavatar	1
allowavatarupload	1
allowavatargallery	1
avatarquality	65
avatarsize	2048
allowimageupload	0
allowimageregupload	1
imageheight	800
imagewidth	800
imagesize	150
allowfileupload	0
allowfileregupload	1
filetypes	zip,txt,doc,gz,tgz
filesize	120
showranking	1
rankimages	1
avatar_src
fb_profile
pm_component
userlist_rows	30
userlist_online	1
userlist_avatar	1
userlist_name	1
userlist_username	1
userlist_posts	1
userlist_karma	1
userlist_email	0
userlist_usertype	0
userlist_joindate	1
userlist_lastvisitdate	1
userlist_userhits	1
latestcategory
showstats	1
showwhoisonline	1
showgenstats	1
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popusercount	5
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popsubjectcount	5
usernamechange	0
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trimlongurlsfront	40
trimlongurlsback	20
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rss_excluded_categories
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fbdefaultpage	categories
default_sort	asc
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sef	1
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polltimebtvotes	00:15:00
pollnbvotesbyuser	100
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ordering_system	mesid
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js_actstr_integration	0
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checkmimetypes	1
imagemimetypes	image/jpeg,image/jpg,image/gif,image/png
imagequality	50
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hideuserprofileinfo	put_empty
integration_access	joomla
integration_login	joomla
integration_avatar	kunena
integration_profile	kunena
integration_private	none
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latestcategory_in	1
topicicons	1
onlineusers	1
debug	0
catsautosubscribed	0
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popthankscount	5
mod_see_deleted	0
bbcode_img_secure	text
listcat_show_moderators	1
lightbox	1
activity_limit	0

Third-party components: AlphaUserPoints: Disabled or not installed | CommunityBuilder: Disabled or not installed | Jomsocial: Disabled or not installed | UddeIm: Disabled or not installed

Plugins: System - Mootools12: Disabled | System - Mootools Upgrade: Disabled | JFirePHP: Disabled or not installed | Kunena Discuss: Disabled or not installed | Kunena Search: Disabled or not installed | My Kunena Forum Menu: Disabled or not installed | My Kunena Forum Posts: Disabled or not installed

Modules: Kunena Latest: Disabled or not installed | Kunena Stats: Disabled or not installed | Kunena Login: Disabled or not installed

Start by disabling legacy mode.

What do you using for sef, the default sef system or a third party component ?