[imp] Unable to open message with attachments

[Lista IMP]

Hi guys,

My setup is as following:

Horde: 3.1
Imp: H3 (4.1) (run Imp tests)
Turba: H3 (2.1.1) (run Turba tests)
PHP Version: 4.3.9
Maildir format with maildrop

Some messages I receive with attachment I cannot open it. When I try
to do so, I receive a blank screen.

Sometimes when I try to send a message with attachments I get the
following error message:
'unable to send data"

Can you help me?