you could try to run hamster from commandline:
/usr/lib/hamster-applet/hamster-applet -w

and look for output!

(In reply to comment #1)
> you could try to run hamster from commandline:
> /usr/lib/hamster-applet/hamster-applet -w
> 
> and look for output!
> 

roni@roni-desktop:~$ /usr/lib/hamster-applet/hamster-applet -w
Running installed hamster, using [/usr/lib/python2.5/site-packages/hamster:$PYTHONPATH]
Data Dir: /usr/share/hamster-applet
SELECT version FROM version None
UPDATE version SET version = 4 ()
select count(*) from categories None
Binding shortcut <Super>H to popup hamster
Running with options: {'do_trace': False, 'standalone': True}
Starting Hamster instance: <gnome.applet.Applet object at 0x84989b4 (PanelApplet at 0x8515000)> None

                   SELECT a.id AS id,
                          a.start_time AS start_time,
                          a.end_time AS end_time,
                          b.name AS name, b.id as activity_id,
                          coalesce(c.name, ?) as category, c.id as category_id
                     FROM facts a
                LEFT JOIN activities b ON a.activity_id = b.id
                LEFT JOIN categories c on b.category_id = c.id
                    WHERE date(a.start_time) >= ? and date(a.start_time) <= ?
                 ORDER BY a.start_time
         ('Unsorted', datetime.date(2008, 8, 13), datetime.date(2008, 8, 13))

                       SELECT *
                         FROM activities
                        WHERE deleted is null
                     ORDER BY lower(name)
             None

                   SELECT a.*, b.category_order
                     FROM activities a
                LEFT JOIN categories b on coalesce(b.id, -1) = a.category_id
                    WHERE a.category_id > -1
                      AND a.deleted is null
                 ORDER BY category_order, activity_order
         None
** (hamster-applet:15523): DEBUG: Opening calendar source uri: file:///home/roni/.evolution/tasks/local/system

** (hamster-applet:15523): DEBUG: Opening calendar source uri: exchange://myuser;auth=Basic@webmail.myworkplace.com/;personal/Tasks

Segmentation fault

check if you have python-evolution package installed. if you have, please uninstall it, since python evolution bindings are now in gnome, and try again.

let us know how it goes!

(In reply to comment #3)
> check if you have python-evolution package installed. if you have, please
> uninstall it, since python evolution bindings are now in gnome, and try again.
> 
> let us know how it goes!
> 

it worked! thanks!

filed bug in Ubuntu (https://bugs.launchpad.net/ubuntu/+source/evolution-python/+bug/257872), closing this one