roundcube 1.3.x, calendar invitation, event could not be imported, service not available, bad request

[pafcioooo]

Sometimes it happens that after receiving calendar invitation in email if:

• I choose calendar check it opens a browser windows with error "SERVICE CURRENTLY NOT AVAILABLE! Error No. [500]""
• if I click accept it shows error "Event could not be imported"

There are errors in public_html/roundcubemail/logs/errors respectively:

• PHP Error: No driver found for calendar "--invitation--itip". (GET /?_task=calendar&view=agendaDay&date=1530795600&itip=INBOX/13418%232%3A0&_extwin=1)
• [02-Jul-2018 04:33:22 +0200]: <bltae9ov> DAV Error: Bad request in /home/poczta/public_html/roundcubemail/plugins/calendar/lib/SabreDAV/lib/OldSabre/DAV/Client.php on line 423 (POST /?_task=calendar&_framed=1&_action=mailimportitip)

Event agenda in email invitation is displayed properly.

[pafcioooo]

Changing:// Enable debugging output for iCAL/CalDAV drivers

$config['calendar_caldav_debug'] = true;
$config['calendar_ical_debug'] = true;

to false doesn not show more in errors file.

[pafcioooo]

There is similiar issue in another repo for this texxasrulez/caldav_calendar#3 but no clear explanation there - this repo seems another fork of this repo apart from one mentioned in #21.

[chaos-prevails]

for me, if you copy the changes of
texxasrulez/caldav_calendar@79eb611#diff-0e51937113ff969af234cc1a48fcadee

over into a clone of repo https://github.com/dotplex/roundcube_calendar
then even the print preview will work.

After that, 2 things still don't work:

1. after accepting an event, clicking "Update in my agenda" I get a Application Error (500): No driver found for calendar "".
2. prior to accepting an event, clicking "check calendar", I get a SERVICE CURRENTLY NOT AVAILABLE! 500

ad 2) deleting the itip parameter of the url fixes the problem. I think "check calendar" should only open the calendar in another window

But the most important functionality works (accept, decline, maybe, delegate) with roundcube 1.3.7

[AkashKrDutta]

You can add a nextcloud calendar URL that works perfectly fine. Problem is every user should be registered there.