Solved Registered users are unable to vote on surveys (polls)

We are having some problems with the surveys (polls) because, since the last times, only moderators and administrators are able to participate on them, while registered user are not allowed. I have been looking for the error but I can not find it. Surely it is something pretty easy but I don't find the key, so I need your help.

This is my conf. report

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

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: 256M | Max file upload: 64M

Kunena menu details:

Warning: Spoiler!

ID	Name	Menutype	Link	Path	In trash
846	Inicio	kunenamenu	view=topics&mode=replies	inicio	No
111	Foros	kunenamenu	view=category&layout=list&catid=0	index	No
112	Temas recientes	kunenamenu	view=topics&mode=replies	recent	No
115	Mis Temas	kunenamenu	view=topics&layout=user&mode=posted	recent/mylatest	No
114	Sin respuesta	kunenamenu	view=topics&mode=noreplies	recent/noreplies	No
118	Buscar	kunenamenu	view=search	buscar	No
206	Usuarios	kunenamenu	view=user&layout=list	user	No
119	Foro	mainmenu	view=home&defaultmenu=111	foro	No
609	Presentaciones y normas	mainmenu	view=category&catid=177	foro/presentaciones-y-normas	No
610	Comunidad Riftmaniaca	mainmenu	view=category&catid=174	foro/comunidad-riftmaniaca	No
611	Área general	mainmenu	view=category&catid=17	foro/comunidad-riftmaniaca/area-general	No
617	Acuarística	mainmenu	view=category&layout=list&catid=18	foro/comunidad-riftmaniaca/acuaristica	No
618	Botica	mainmenu	view=category&layout=list&catid=47	foro/comunidad-riftmaniaca/botica	No
619	Bricolaje	mainmenu	view=category&layout=list&catid=46	foro/comunidad-riftmaniaca/bricolaje	No
613	Malawi	mainmenu	view=category&layout=list&catid=171	foro/malawi	No
614	Tanganyika	mainmenu	view=category&catid=172	foro/tanganyika	No
615	Victoria y adyacentes	mainmenu	view=category&layout=list&catid=173	foro/victoria-y-adyacentes	No
616	Madagascar y fluviales	mainmenu	view=category&layout=list&catid=175	foro/madagascar-y-fluviales	No
612	Compra, venta e intercambio	mainmenu	view=category&catid=181	foro/compra-venta-e-intercambio	No

Joomla default template details : findelat | author: findelat | version: 1.0 | creationdate: 02/02/2015

Kunena default template details : Blue Eagle | author: Kunena Team | version: 4.0.12 | creationdate: 2016-10-01

Kunena version detailed: Kunena 4.0.12 | 2016-10-01 [ Lima ]
| Kunena detailed configuration:

Warning: Spoiler!

Kunena config settings:
board_offline	0
enablerss	1
threads_per_page	20
messages_per_page	10
messages_per_page_search	25
showhistory	1
historylimit	25
shownew	1
disemoticons	0
template	blue_eagle
showannouncement	1
avataroncat	1
catimagepath	category_images
showchildcaticon	0
rtewidth	450
rteheight	400
enableforumjump	1
reportmsg	1
username	1
askemail	0
showemail	0
showuserstats	1
showkarma	0
useredit	1
useredittime	3600
useredittimegrace	7200
editmarkup	0
allowsubscriptions	1
subscriptionschecked	0
allowfavorites	1
maxsubject	63
maxsig	300
regonly	0
pubwrite	0
floodprotection	0
mailmod	0
mailadmin	0
captcha	0
mailfull	0
allowavatarupload	1
allowavatargallery	0
avatarquality	75
avatarsize	6048
imageheight	1200
imagewidth	1200
imagesize	3050
filetypes	docx,doc,txt,rtf,pdf,xls,xlsx,ppt,jpg
filesize	64000
showranking	1
rankimages	1
userlist_rows	30
userlist_online	1
userlist_avatar	1
userlist_posts	1
userlist_karma	0
userlist_email	0
userlist_joindate	1
userlist_lastvisitdate	1
userlist_userhits	0
latestcategory	0
showstats	1
showwhoisonline	1
showgenstats	1
showpopuserstats	1
popusercount	6
showpopsubjectstats	1
popsubjectcount	10
showspoilertag	0
showvideotag	0
showebaytag	0
trimlongurls	1
trimlongurlsfront	30
trimlongurlsback	15
autoembedyoutube	1
autoembedebay	0
ebaylanguagecode	es-es
sessiontimeout	4800
highlightcode	1
rss_type	topic
rss_timelimit	month
rss_limit	100
rss_included_categories
rss_excluded_categories
rss_specification	rss2.0
rss_allow_html	1
rss_author_format	name
rss_author_in_title	1
rss_word_count	0
rss_old_titles	1
rss_cache	900
defaultpage	recent
default_sort	asc
sef	1
showimgforguest	1
showfileforguest	1
pollnboptions	10
pollallowvoteone	1
pollenabled	1
poppollscount	5
showpoppollstats	1
polltimebtvotes	00:00:05
pollnbvotesbyuser	1
pollresultsuserslist	1
maxpersotext	50
ordering_system	replyid
post_dateformat	datetime
post_dateformat_hover	datetime
hide_ip	1
imagetypes	jpg,jpeg,gif,png
checkmimetypes	1
imagemimetypes	image/jpeg,image/jpg,image/gif,image/png
imagequality	50
thumbheight	32
thumbwidth	32
hideuserprofileinfo	put_empty
boxghostmessage	0
userdeletetmessage	0
latestcategory_in	1
topicicons	1
debug	0
catsautosubscribed	0
showbannedreason	0
showthankyou	1
showpopthankyoustats	1
popthankscount	5
mod_see_deleted	0
bbcode_img_secure	text
listcat_show_moderators	0
lightbox	1
show_list_time	720
show_session_type	0
show_session_starttime	0
userlist_allowed	1
userlist_count_users	3
enable_threaded_layouts	0
category_subscriptions	post
topic_subscriptions	every
pubprofile	0
thankyou_max	10
email_recipient_count	0
email_recipient_privacy	bcc
captcha_post_limit	0
keywords	0
userkeywords	0
image_upload	everybody
file_upload	moderator
topic_layout	flat
time_to_create_page	0
show_imgfiles_manage_profile	0
hold_newusers_posts	0
hold_guest_posts	0
attachment_limit	6
pickup_category	0
article_display	intro
send_emails	1
fallback_english	1
cache	1
cache_time	180
iptracking	1
rss_feedburner_url
autolink	1
access_component	1
statslink_allowed	1
superadmin_userlist	0
legacy_urls	1
attachment_protection	1
categoryicons	1
avatarresizemethod	1
avatarcrop	0
user_report	1
searchtime	all
teaser	1
ebay_language	0
twitter_consumer_key
twitter_consumer_secret
allow_change_subject	1
max_links	12
userlist_name	0
usernamechange	0
version_check	1
userlist_usertype	0
sefutf8	0

| Kunena integration settings:

Warning: Spoiler!

Kunena - AlphaUserPoints Disabled
Kunena - Community Builder Disabled
Kunena - Gravatar Disabled
Kunena - JomSocial Disabled
Kunena - Joomla Enabled: access=1 login=1
Kunena - Kunena Enabled: avatar=1 profile=1
Kunena - UddeIM Enabled: private=1

| Joomla! detailed language files installed:

Warning: Spoiler!

Joomla! languages installed:
es-ES	Spanish (español)
en-GB	English (en-GB)

Third-party components: UddeIM 3.7

Third-party SEF components: None

Plugins: Search - Kunena Search 3.1.2

Modules: Kunena Latest 3.1.2.1 | Kunena Login 3.1.2

I'm sorry, but Kunena 4.0.12 is not supported anymore. It has never been tested with Joomla 3.8, so we don't know, what is the cause for your problem.

Thank you for your answer. I will try to find out how to fix it. This problem comes from six months ago, at least