Tracker : blank page since upgrade to 1.6

Hi,

I've recently upgraded my egroupware installation to 1.6.
Everything seems to be working fine except the tracker module.
I can create new items, I can list them but I can't change them : when I click on the description to open the item, I get a popup that stays blank.

I've updated my installation with svn, but the problem still occurs.

Here's my apache log :

[Wed Jan 14 15:18:03 2009] [error] [client 172.16.100.50] PHP Warning:  Can't load stream-wrapper for scheme 'links'! in /var/www/web1/web/egroupware/phpgwapi/inc/class.vfs_stream_wrapper.inc.php on line 760, referer: https://localhost/egroupware/etemplate/process_exec.php?menuaction=tracker.tracker_ui.index
[Wed Jan 14 15:18:03 2009] [error] [client 172.16.100.50] PHP Warning:  filectime() [function.filectime]: stat failed for /var/www/web1/web/egroupware/etemplate/js/etemplate.js in /var/www/web1/web/egroupware/etemplate/inc/class.etemplate.inc.php on line 2166, referer: https://localhost/egroupware/etemplate/process_exec.php?menuaction=tracker.tracker_ui.index
[Wed Jan 14 15:18:03 2009] [error] [client 172.16.100.50] PHP Warning:  filemtime() [function.filemtime]: stat failed for /var/www/web1/web/egroupware/etemplate/templates/default/app.css in /var/www/web1/web/egroupware/etemplate/inc/class.etemplate.inc.php on line 249, referer: https://localhost/egroupware/etemplate/process_exec.php?menuaction=tracker.tracker_ui.index
[Wed Jan 14 15:18:03 2009] [error] [client 172.16.100.50] PHP Fatal error:  Class 'egw_exception_wrong_parameter' not found in /var/www/web1/web/egroupware/phpgwapi/inc/class.Template.inc.php on line 475, referer: https://localhost/egroupware/etemplate/process_exec.php?menuaction=tracker.tracker_ui.index


I've been searching for serveral hours now, but I'm stuck, I don't know what to do.
Any idea on what could be wrong in my egroupware installation ?


Kindest regards,
Matthieu