[horde] Recipient cannot accept appointment, DB error?

[Andreas Mauser]

Dear Team,

I hope I got the correct log entry, but the CLient receives an error when accepting my Horde calender invite:

Beschäftigt
Serverfehler beim Abfragen der Datenbank.

In the logs I then see:

2022-03-19T22:53:59+01:00 DEBUG: HORDE Max memory usage: 2097152 bytes [pid 2134483 on line 613 of "/usr/share/php/Horde/Registry.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE Load config file (conf.php; app: horde) [pid 2137234 on line 109 of "/usr/share/php/Horde/Registry/Loadconfig.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE Connected to the following memcache servers:localhost:11211 [pid 2137234 on line 205 of "/usr/share/php/Horde/Memcache.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE Horde_HashTable_Memcache: Retrieved keys (68dnccsslau2h13p57fd1hqhul) [pid 2137234 on line 232 of "/usr/share/php/Horde/HashTable/Base.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE Read session data (68dnccsslau2h13p57fd1hqhul) [pid 2137234]
2022-03-19T22:54:00+01:00 DEBUG: HORDE [kronolith] Load config file (conf.php; app: kronolith) [pid 2137234 on line 109 of "/usr/share/php/Horde/Registry/Loadconfig.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE [kronolith] Horde_Prefs: Storing preference value (display_external_cals) [pid 2137234 on line 532 of "/var/www/html/post/kronolith/lib/CalendarsManager.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE [kronolith] PHP ERROR: The each() function is deprecated. This message will be suppressed on further calls [pid 2137234 on line 40 of "/usr/share/php/Horde/History/Log.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE  1. Kronolith_Event->save() /var/www/html/post/kronolith/attend.php:58
 2. Kronolith_Driver->saveEvent() /var/www/html/post/kronolith/lib/Event.php:648
 3. Kronolith_Driver_Sql->_updateEvent() /var/www/html/post/kronolith/lib/Driver.php:370
 4. Horde_Core_History->log() /var/www/html/post/kronolith/lib/Driver/Sql.php:635
 5. Horde_History->log() /usr/share/php/Horde/Core/History.php:76
 6. Horde_History->getHistory() /usr/share/php/Horde/History.php:115
 7. Horde_History_Sql->_getHistory() /usr/share/php/Horde/History.php:170
 8. Horde_History_Log->__construct() /usr/share/php/Horde/History/Sql.php:170
 9. each() /usr/share/php/Horde/History/Log.php:40
10. Horde_ErrorHandler::errorHandler()

2022-03-19T22:54:00+01:00 DEBUG: HORDE [kronolith] Load config file (prefs.php; app: kronolith) [pid 2137234 on line 109 of "/usr/share/php/Horde/Registry/Loadconfig.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE [kronolith] Load config file (nls.php; app: horde) [pid 2137234 on line 109 of "/usr/share/php/Horde/Registry/Loadconfig.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE [kronolith] Load config file (prefs.php; app: horde) [pid 2137234 on line 109 of "/usr/share/php/Horde/Registry/Loadconfig.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE [kronolith] Sending event notifications for Beschäftigt to Mausers <andreas at mausers.info> [pid 2137234 on line 2207 of "/var/www/html/post/kronolith/lib/Kronolith.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE [imp] Load config file (conf.php; app: imp) [pid 2137234 on line 109 of "/usr/share/php/Horde/Registry/Loadconfig.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE [imp] Load config file (backends.php; app: imp) [pid 2137234 on line 109 of "/usr/share/php/Horde/Registry/Loadconfig.php"]
2022-03-19T22:54:00+01:00 ERR: HORDE [kronolith] SQL QUERY FAILED: SQLSTATE[22007]: Invalid datetime format: 1292 Truncated incorrect DOUBLE value: 'andreas'  
	UPDATE `horde_alarms` SET `alarm_start` = ?, `alarm_end` = ?,
	  `alarm_methods` = ?, `alarm_params` = :binary0, `alarm_title` = ?,
	  `alarm_instanceid` = ?, `alarm_text` = ?, `alarm_snooze` = ?,
	  `alarm_dismissed` = ? WHERE alarm_id =
	  '20220317104955.ln1V0MScKxreV-cGvaJvC8t at post.mauser.info' AND
	  alarm_uid = 0 [pid 2137234 on line 289 of "/usr/share/php/Horde/Db/Adapter/Pdo/Base.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE [kronolith] Max memory usage: 2097152 bytes [pid 2137234 on line 613 of "/usr/share/php/Horde/Registry.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE [kronolith] Horde_HashTable_Memcache: Set key (68dnccsslau2h13p57fd1hqhul) [pid 2137234 on line 288 of "/usr/share/php/Horde/HashTable/Base.php"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE [kronolith] Wrote session data (68dnccsslau2h13p57fd1hqhul) [pid 2137234]
2022-03-19T22:54:00+01:00 WARN: HORDE [kronolith] PHP ERROR: Cannot modify header information - headers already sent [pid 2137234 on line 0 of "Unknown"]
2022-03-19T22:54:00+01:00 DEBUG: HORDE 1. Horde_ErrorHandler::errorHandler()

What may be wrong here and where should I start looking?

Many thanks,
Andreas