[horde] MacOs CalDav Client fails connection with error 500

[Horst Simon]

I have imported contacts from an ics file into the horde web interface
calendar and when i connect with the macOs client it shows only a few
entries and gives an error 500. When I check the horde log I get an error
on timezone, maybe a configuration issue or something missing? Horde log
attached.

Horst
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HORDE 2026-09-29T15:26:10+10:00 error: [kronolith] ValueError: Unknown format specifier "z" in /opt/local/www/apache2/horde/vendor/horde/timezone/lib/Horde/Timezone/Rule.php:243
Stack trace:
#0 /opt/local/www/apache2/horde/vendor/horde/timezone/lib/Horde/Timezone/Rule.php(243): sprintf()
#1 /opt/local/www/apache2/horde/vendor/horde/timezone/lib/Horde/Timezone/Zone.php(126): Horde_Timezone_Rule->addRules()
#2 /opt/local/www/apache2/horde/vendor/horde/kronolith/lib/Event.php(760): Horde_Timezone_Zone->toVtimezone()
#3 /opt/local/www/apache2/horde/vendor/horde/kronolith/lib/Application.php(1067): Kronolith_Event->toiCalendar()
#4 /opt/local/www/apache2/horde/vendor/horde/core/lib/Horde/Registry.php(1328): Kronolith_Application->davGetObject()
#5 /opt/local/www/apache2/horde/vendor/horde/dav/lib/Horde/Dav/Calendar/Backend.php(154): Horde_Registry->callAppMethod()
#6 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/CalDAV/Backend/AbstractBackend.php(54): Horde_Dav_Calendar_Backend->getCalendarObject()
#7 [internal function]: Sabre\CalDAV\Backend\AbstractBackend->{closure:Sabre\CalDAV\Backend\AbstractBackend::getMultipleCalendarObjects():53}()
#8 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/CalDAV/Backend/AbstractBackend.php(53): array_map()
#9 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/CalDAV/Calendar.php(144): Sabre\CalDAV\Backend\AbstractBackend->getMultipleCalendarObjects()
#10 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/DAV/Tree.php(294): Sabre\CalDAV\Calendar->getMultipleChildren()
#11 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/DAV/Server.php(1035): Sabre\DAV\Tree->getMultipleNodes()
#12 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/CalDAV/Plugin.php(437): Sabre\DAV\Server->getPropertiesForMultiplePaths()
#13 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/CalDAV/Plugin.php(253): Sabre\CalDAV\Plugin->calendarMultiGetReport()
#14 /opt/local/www/apache2/horde/vendor/sabre/event/lib/WildcardEmitterTrait.php(89): Sabre\CalDAV\Plugin->report()
#15 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/DAV/CorePlugin.php(695): Sabre\DAV\Server->emit()
#16 /opt/local/www/apache2/horde/vendor/sabre/event/lib/WildcardEmitterTrait.php(89): Sabre\DAV\CorePlugin->httpReport()
#17 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/DAV/Server.php(472): Sabre\DAV\Server->emit()
#18 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/DAV/Server.php(253): Sabre\DAV\Server->invokeMethod()
#19 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/DAV/Server.php(321): Sabre\DAV\Server->start()
#20 /opt/local/www/apache2/horde/vendor/horde/rpc/lib/Horde/Rpc/Webdav.php(67): Sabre\DAV\Server->exec()
#21 /opt/local/www/apache2/horde/vendor/horde/horde/rpc.php(202): Horde_Rpc_Webdav->getResponse()
#22 /opt/local/www/apache2/horde/web/horde/rpc.php(3): require_once('...')
#23 {main} [pid 492 on line 154 of "/opt/local/www/apache2/horde/vendor/horde/dav/lib/Horde/Dav/Calendar/Backend.php"]
HORDE 2026-09-29T15:26:16+10:00 error: [kronolith] ValueError: Unknown format specifier "z" in /opt/local/www/apache2/horde/vendor/horde/timezone/lib/Horde/Timezone/Rule.php:243
Stack trace:
#0 /opt/local/www/apache2/horde/vendor/horde/timezone/lib/Horde/Timezone/Rule.php(243): sprintf()
#1 /opt/local/www/apache2/horde/vendor/horde/timezone/lib/Horde/Timezone/Zone.php(126): Horde_Timezone_Rule->addRules()
#2 /opt/local/www/apache2/horde/vendor/horde/kronolith/lib/Event.php(760): Horde_Timezone_Zone->toVtimezone()
#3 /opt/local/www/apache2/horde/vendor/horde/kronolith/lib/Application.php(1067): Kronolith_Event->toiCalendar()
#4 /opt/local/www/apache2/horde/vendor/horde/core/lib/Horde/Registry.php(1328): Kronolith_Application->davGetObject()
#5 /opt/local/www/apache2/horde/vendor/horde/dav/lib/Horde/Dav/Calendar/Backend.php(154): Horde_Registry->callAppMethod()
#6 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/CalDAV/Backend/AbstractBackend.php(54): Horde_Dav_Calendar_Backend->getCalendarObject()
#7 [internal function]: Sabre\CalDAV\Backend\AbstractBackend->{closure:Sabre\CalDAV\Backend\AbstractBackend::getMultipleCalendarObjects():53}()
#8 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/CalDAV/Backend/AbstractBackend.php(53): array_map()
#9 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/CalDAV/Calendar.php(144): Sabre\CalDAV\Backend\AbstractBackend->getMultipleCalendarObjects()
#10 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/DAV/Tree.php(294): Sabre\CalDAV\Calendar->getMultipleChildren()
#11 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/DAV/Server.php(1035): Sabre\DAV\Tree->getMultipleNodes()
#12 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/CalDAV/Plugin.php(437): Sabre\DAV\Server->getPropertiesForMultiplePaths()
#13 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/CalDAV/Plugin.php(253): Sabre\CalDAV\Plugin->calendarMultiGetReport()
#14 /opt/local/www/apache2/horde/vendor/sabre/event/lib/WildcardEmitterTrait.php(89): Sabre\CalDAV\Plugin->report()
#15 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/DAV/CorePlugin.php(695): Sabre\DAV\Server->emit()
#16 /opt/local/www/apache2/horde/vendor/sabre/event/lib/WildcardEmitterTrait.php(89): Sabre\DAV\CorePlugin->httpReport()
#17 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/DAV/Server.php(472): Sabre\DAV\Server->emit()
#18 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/DAV/Server.php(253): Sabre\DAV\Server->invokeMethod()
#19 /opt/local/www/apache2/horde/vendor/sabre/dav/lib/DAV/Server.php(321): Sabre\DAV\Server->start()
#20 /opt/local/www/apache2/horde/vendor/horde/rpc/lib/Horde/Rpc/Webdav.php(67): Sabre\DAV\Server->exec()
#21 /opt/local/www/apache2/horde/vendor/horde/horde/rpc.php(202): Horde_Rpc_Webdav->getResponse()
#22 /opt/local/www/apache2/horde/web/horde/rpc.php(3): require_once('...')
#23 {main} [pid 1326 on line 154 of "/opt/local/www/apache2/horde/vendor/horde/dav/lib/Horde/Dav/Calendar/Backend.php"]