[imp] Errors when displaying mail

[ES]

Hello List,
Im using:
SuSE-Linux 8.2
apache-1.3.27-38
mod_php-4.3.1
mod_php-core-4.3.1
horde-2.2.4
imp-3.2.2

When viewing Inbox, Sent or Trash listviews and selecting one message 
with a doubleclick on subject or sender the message will either be 
displayed with the following message at the top:
"Notice: Undefined offset: -6 in /srv/www/htdocs/horde/imp/message.php 
on line 273"
The offsetvalue depends on which message one wants to open and varies 
with values like -1, -6 or 11 in my case.
or
the message will not be displayed at all  with the following message in 
the normal "Errorline" in the inbox view::
"There was an error viewing the requested message."

Any hints?
Greetings from germany
ES