I have exactly the same problem. Since upgrading to KDE 4.8.3 I get this error whenever akondi checks for updates.

I updated another computer to KDE 4.8.3, and I get the same popups.
This is getting annoying.

I have build a kdepim runtime package with this changeset removed:
https://projects.kde.org/projects/kde/kdepim-runtime/repository/revisions/77d63ae37d53a811785978a450e6f722dbb9655e/diff/resources/dav/protocols/carddavprotocol.cpp


the error seems to be fixed with that.

(In reply to comment #3)
> I have build a kdepim runtime package with this changeset removed:
> https://projects.kde.org/projects/kde/kdepim-runtime/repository/revisions/
> 77d63ae37d53a811785978a450e6f722dbb9655e/diff/resources/dav/protocols/
> carddavprotocol.cpp
> 
> 
> the error seems to be fixed with that.

After some trying out I can confirm that removing this changeset also removes the weird "errors".

I have two user accounts on the same computer.
User 1 is completely local, and akonadi operates on a per-user local mysql instance, and the bug happens.
The interesting part is user 2, which uses a central mysql server for akonadi because its home directory is on nfs... and the bug does **not** happen.

I can confirm that removing this patch set also solved the problem for me, although I don't know what the original intent of the introduced change was. I forgot to mention that I'm also working with owncloud.

I am experiencing a similar effect with ownCloud **contacts** (not with calendars) on Kubuntu 12.04 with kdepim-runtime 4:4.8.3-0ubuntu0.1~ppa1.  The caldav sync works fine.  However, whenever the carddav sync kicks in, I get this popup with the error message described above and no contacts are synced at all.  For me downgrading to kdepim-runtime 4:4.8.2a-0ubuntu2 helps in bringing the carddav sync with my ownCloud instance back to working properly.

Same here, downgrading to kdepim-runtime 4.8.2 fix the issue...

Building kdepim-runtime-4.8.3 ArchLinux package reverting 77d63ae37d53a811785978a450e6f722dbb9655e commit also fix the issue.

*** Bug 300047 has been marked as a duplicate of this bug. ***

I'll try to give a look into this this week. If any of you can attach to this bug, or send me privately, a network capture of what's going on between the resource and the server this would definitely help speed things up. The full error message (there's a number between brackets after "unknown error code 0"; this last number means nothing resource-wise).

Same here I reverted kdepim-runtime to 4.8.2a in kubuntu 12.04 and it got fixed. I also filled a bug in launchpad about this bug: https://bugs.launchpad.net/ubuntu/+source/kdepim/+bug/998179

I know that this doesn't bring much information but I didn't find a good (and easy) way of following comments on this bug, other than commenting. It would be great if there were a button of "follow me" in bugs.kde.org

I wonder if I should fill a bug for that...

Git commit bec63a313160ec6dc1833029d5e99746779ed3f4 by Gregory Oestreicher.
Committed on 15/05/2012 at 21:19.
Pushed by goestreicher into branch 'KDE/4.8'.

Add a prop-filter in the CardDAV requests
FIXED-IN: 4.8.4

M  +6    -0    resources/dav/protocols/carddavprotocol.cpp

http://commits.kde.org/kdepim-runtime/bec63a313160ec6dc1833029d5e99746779ed3f4

Hi,

Both reverting the previous patch or applying this one on kdepim-runtime 4.8.3 does not fix the bug for me.
It should be said that I reported the bug #300047 that was marked as duplicate and that I never experienced the "unknown error code 0" message box!

Thus, I am wondering if #300047 is really a duplicate :)

>I never experienced the "unknown error code 0" message box!

Same for me, message is in akonadiconsole debug tools...

For information, I don't have this error message in the console debug tool either, I just get what I pasted below. I am going to answer the question on the other bug report as soon as I get the information from the admins.

akonadi_davgroupware_resource_8 (0x1d2afb0) 1313 LSUB 411 0 (RESOURCE akonadi_davgroupware_resource_8) (ANCESTORS INF) 
akonadi_davgroupware_resource_8 (0x1d2afb0) * 411 409 (NAME "Perso" MIMETYPE (text/directory) REMOTEID "https://hostname/SOGo/dav/username/Contacts/personal/" REMOTEREVISION "" RESOURCE "akonadi_davgroupware_resource_8" CACHEPOLICY (INHERIT true INTERVAL 3 CACHETIMEOUT -1 SYNCONDEMAND false LOCALPARTS ()) ANCESTORS ((409 "akonadi_davgroupware_resource_8") (0 "")) ENTITYDISPLAY "(\"\" \"view-pim-contacts\" \"\" ())" AccessRights "a" davprotocol "1") 
akonadi_davgroupware_resource_8 (0x1d2afb0) 1313 OK List completed 
akonadi_davgroupware_resource_8 (0x1d2afb0) 1314 SELECT SILENT 411 
akonadi_davgroupware_resource_8 (0x1d2afb0) 1314 OK Completed 
akonadi_davgroupware_resource_8 (0x1d2afb0) 1315 FETCH 1:* FULLPAYLOAD ALLATTR CACHEONLY EXTERNALPAYLOAD (UID REMOTEID REMOTEREVISION COLLECTIONID FLAGS SIZE DATETIME) 
akonadi_davgroupware_resource_8 (0x1d2afb0) 1315 OK FETCH completed

I am getting a message "Yahoo!: Die Elemente können nicht empfangen werden: caldav.calendar.yahoo.com" (~"... the elements cannot be received ...") in KDE 4.8.3 (Ubuntu 12.04). Could this be the same issue, or shall I open a new bug?

Created attachment 71527 [details]
kde-akonadi-bug.png

(In reply to comment #17)
Send me a screeenshot of the error, but it's unlikely to be the same issue if it's happening with a calendar.

Am Samstag, 2. Juni 2012, 16:50:26 schrieben Sie:
> https://bugs.kde.org/show_bug.cgi?id=299482
> 
> --- Comment #18 from Grégory Oestreicher <greg@kamago.net> ---
> (In reply to comment #17)
> Send me a screeenshot of the error, but it's unlikely to be the same issue
> if it's happening with a calendar.
The error message comes as a Plasma notification. Please find the screenshot 
attached.

--Dennis

If I add a new owncloud 4.5 CalDAV ressource on 4.10, I get a similar error on the test connection page:
An error occurred: There was a problem with the request. Unknown error code 0 Please send a full bug report at http://bugs.kde.org. (405).

 Needless to say: thunderbird with lightning plugin works perfectly. How can I help to debug this?

(In reply to comment #20)
> If I add a new owncloud 4.5 CalDAV ressource on 4.10, I get a similar error
> on the test connection page:
> An error occurred: There was a problem with the request. Unknown error code
> 0 Please send a full bug report at http://bugs.kde.org. (405).

It's unlikely to be the same issue, could you please open a separate bug? The HTTP 405 code means that the method is not allowed (I guess this was in a response to a propfind). Could you check that the URL is indeed correct?