NextCloud 14, Calendar - errors in requests to share links

Hello
We are have:

In Nextcloud was installed app the Calendar

When created a new calendar, pushed button share link - and send via email to user.
Now, when user open the link in his browser and push button - “subscribe” - then show pop-up message -
“Unable to create io-slave. klauncher said: Could not find the ‘kio_http’ plugin”

And we are have error messeges in log:

Fatal   webdav   Sabre\DAV\Exception\BadRequest: Calendar object with uid already exists in this calendar collection.
/var/www/html/3rdparty/sabre/dav/lib/CalDAV/Calendar.php - line 201:

OCA\DAV\CalDAV\CalDavBackend->createCalendarObject("12", "Nextcloud-K ... s", "BEGIN:VCALE ... R")

/var/www/html/3rdparty/sabre/dav/lib/DAV/Server.php - line 1096:

Sabre\CalDAV\Calendar->createFile("Nextcloud-K ... s", "BEGIN:VCALE ... R")

/var/www/html/3rdparty/sabre/dav/lib/DAV/CorePlugin.php - line 529:

Sabre\DAV\Server->createFile("calendars/m ... s", "BEGIN:VCALE ... R", null)

Sabre\DAV\CorePlugin->httpPut(Sabre\HTTP\R ... "}, Sabre\HTTP\Response {})

/var/www/html/3rdparty/sabre/event/lib/EventEmitterTrait.php - line 105:

call_user_func_array([ Sabre\DAV\ ... "], [ Sabre\HTTP ... }])

/var/www/html/3rdparty/sabre/dav/lib/DAV/Server.php - line 479:

Sabre\Event\EventEmitter->emit("method:PUT", [ Sabre\HTTP ... }])

/var/www/html/3rdparty/sabre/dav/lib/DAV/Server.php - line 254:

Sabre\DAV\Server->invokeMethod(Sabre\HTTP\R ... "}, Sabre\HTTP\Response {})

/var/www/html/apps/dav/lib/Server.php - line 293:

Sabre\DAV\Server->exec()

/var/www/html/apps/dav/appinfo/v2/remote.php - line 35:

OCA\DAV\Server->exec()

/var/www/html/remote.php - line 163:

require_once("/var/www/ht ... p")