$vEventException_r = $exceptionEvent->toiCalendar($calendar);

While I do not run the latest Horde checkout, I backported the fix you 
committed. The problem persists; I traced it to an OutOfMemory-problem:

In kronolith/lib/Api.php, line 896 onward, I wrote:
`$i=-1;
             foreach ($events as $dayevents) {
print(++$i.'<br/>');
print((memory_get_usage()/1024/1024).'MB / '. ini_get('memory_limit') 
. '<br/>');
                 foreach ($dayevents as $event) {
                     $iCal->addComponent($event->toiCalendar($iCal));
                 }
             }
die();
`

From this I deduced I exceeded the memory limit. I find it dubious 
that experting a mere 100 calendar entries would require 184MB to 
yield a 2.9MB file; can we optimize this?

In Icalendar.php, we can (at least) do this:
`
     public function addComponent(&$components)
     {
         if (is_array($components)) {
             foreach ($components as &$component) {
                 $this->addComponent($component);
             }
         } else if ($components instanceof Horde_Icalendar) {
             $components->_container = &$this;
             $this->_components[] = &$components;
         }
     }

`
Notice the ampersands; i.e., by-reference/address-of operator. The 
line "$this->_components[] = &$component;" is still the most expensive 
one. Anyhow, by replacing addComponent as such, we cut down memory 
usage from 184MB to 53MB (and gain more performance as well)!

I recommend exploring further applications of passing values 
by-reference (by using the &-operator) instead of by-value throughout 
Horde (especially oft-used functions, like domain-entity functions).




-----------


Also, the previous fix for kronolith/lib/Event.php you added checks 
for the Timezone-object being at index 0 or 1, but array_pop always 
retrieves the object at the last index (rather than the non-Timezone 
index). I suggest the following generalization:
`
                     foreach ($vEventException_r as $key => &$vEE){
                         if ($vEE instanceof Horde_Icalendar_Vtimezone){
                             unset($vEventException_r[$key]);
                         }
                     }
                     // This should never happen, but protect against 
it anyway.
                     if (count($vEventException_r) > 1) {
                         throw new Kronolith_Exception(_("Unable to 
parse event."));
                     }
                     $vEventException = array_pop($vEventException_r);
`

This is fine, exceptions to recurring events are separate VEVENT entries.
Works perfectly fine for me with a current Horde checkout even with 
the other ICS file.

Alas, it seems the problem is not completely solved.

* CalDAV counts 551 entries in its index, while the database and 
source ICS-file contain 595 entries. Unless not all VEVENT-objects 
should be in the index, there is still a problem here.
* The ICAL-URL is completely empty, supposedly because PHP's request 
handling died prematurely.

I will contact Jan via e-mail about a larger ICS-file with which the 
problem can be reproduced.

Changes have been made in Git (master):

commit ecd18ac4f04036cf6cede10be1c30c5d901edc5c
Author: Jan Schneider <jan@horde.org>
Date:   Tue Oct 29 18:44:02 2013 +0100

     [jan] Fix fatal error if recurrence exceptions have timezones set 
(Bug #12801).

  kronolith/docs/CHANGES  |    1 +
  kronolith/lib/Event.php |    5 ++++-
  kronolith/package.xml   |    4 ++--
  3 files changed, 7 insertions(+), 3 deletions(-)

http://git.horde.org/horde-git/-/commit/ecd18ac4f04036cf6cede10be1c30c5d901edc5c