[horde] Horde stopped working after upgrade

[Arjen de Korte]

After running

    pear upgrade -c horde

tonight, horde stopped working completely. Whatever I try, I get
something like the following in the Apache logs:

[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP Fatal
error:  Call to a member function setObs() on a non-object in
/usr/share/php5/PEAR/Horde/Perms/Sql.php on line 130, referer:
https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP Stack
trace:, referer: https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP   1.
{main}() /srv/www/htdocs/horde/test.php:0, referer:
https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP   2.
Horde_Registry->pushApp() /srv/www/htdocs/horde/test.php:83, referer:
https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP   3.
Horde_Registry->callAppMethod()
/usr/share/php5/PEAR/Horde/Registry.php:1546, referer:
https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP   4.
call_user_func_array() /usr/share/php5/PEAR/Horde/Registry.php:1141,
referer: https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP   5.
Horde_Registry_Application->init()
/usr/share/php5/PEAR/Horde/Registry.php:1141, referer:
https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP   6.
Kronolith_Application->_init()
/usr/share/php5/PEAR/Horde/Registry/Application.php:105, referer:
https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP   7.
Kronolith::initialize()
/srv/www/htdocs/horde/kronolith/lib/Application.php:75, referer:
https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP   8.
Kronolith::hasApiPermission()
/srv/www/htdocs/horde/kronolith/lib/Kronolith.php:907, referer:
https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP   9.
Horde_Registry->hasPermission()
/srv/www/htdocs/horde/kronolith/lib/Kronolith.php:3068, referer:
https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP  10.
Horde_Perms_Base->hasPermission()
/usr/share/php5/PEAR/Horde/Registry.php:1659, referer:
https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP  11.
Horde_Perms_Base->getPermissions()
/usr/share/php5/PEAR/Horde/Perms/Base.php:249, referer:
https://www.example.com/horde/test.php
[Tue Mar 05 22:03:19 2013] [error] [client 192.168.1.121] PHP  12.
Horde_Perms_Sql->getPermission()
/usr/share/php5/PEAR/Horde/Perms/Base.php:144, referer:
https://www.example.com/horde/test.php
192.168.1.121 - - [05/Mar/2013:22:03:19 +0100] "GET
/horde/test.php?app=kronolith HTTP/1.1" 200 -

I have no idea what went wrong and in which direction I should be
looking for a solution. Any ideas?