[imp] [Horde] Strip attachment problem

[HHHKKK]

Hi,
I have just reinstalled Horde via pear on a new server and I have a  php
problem.

When users try to delete attachment from emails, we have a blank page and
there are apache logs :
[Fri Aug 24 11:15:16 2012] [error] [client 10.0.24.1] PHP Fatal error: Call
to a member function push() on a non-object in
/var/www/horde/imp/message.php on line 197, referer:
https://10.0.0.5/horde/imp/message.php?mailbox=SU5CT1g
<https://10.0.0.5/horde/imp/message.php?mailbox=SU5CT1g&uid=33> &uid=33
[Fri Aug 24 11:15:16 2012] [error] [client 10.0.24.1] PHP Fatal error: Call
to a member function set() on a non-object in
/var/www/horde/imp/lib/Factory/Mailbox.php on line 84, referer:
https://10.0.0.5/horde/imp/message.php?mailbox=SU5CT1g
<https://10.0.0.5/horde/imp/message.php?mailbox=SU5CT1g&uid=33> &uid=33

what can we do for this problem ?
Thanks.