[imp] Strange problems with Attachments sent from Outlook logging me out.

[jonathan soong]

Hi Guys,

I'm having a strange problem with attachments - under certain 
circumstances, clicking on an attachment (a CSV file in my case) will 
cause the session to be destroyed and i will be directed to the login 
screen.

I believe it has to do with the mailer sending the file.

I have sent myself the same file from the Webmail interface (using both 
IE6 and Mozilla 1.4), Mozilla mail client (bundled with Mozilla 1.4) and 
Outlook.

 From the Webmail Interface and Mozilla, all is fine.

 From Outlook, i get directed to the login screen.

Setup:
horde 2.2.3
imp 3.2.1

Details::
++ When i receive mail that has been sent from Mozilla, the CSV file is 
actually displayed under the body of the message in Webmail (i.e. it 
parses the file and displays it) - I also have the links to view it or 
download it.

++When i receive mail that has been sent from Webmail, the CSV file is 
NOT displayed under the body of the message but the links to view it and 
download it work.

++When i receive mail that has been sent from Outlook, the CSV file is 
NOT displayed under the body of the message and the links to view it and 
download it are redirected to the login prompt (if i click the 'View' 
link it opens a new window with the login prompt, if i click the 
'Download' link it opens a login prompt in the same window). In both 
cases it gives the reason as "Your Mail session has expired. Please 
login again."
-- If i now login, i get an error:  "*Notice*: Undefined index: in 
*/usr/local/apache_1.3.28/htdocs/horde-2.2.3/imp/view.php* on line *35" 
*(this is "$mime = $attachments[Horde::getFormData('id')];")*, *however 
i believe the authentication works in this instance - i can click 'back' 
and if i now reopen the email with the CSV attachment, i can now access 
it with no problems.

Any help with this would be most appreciated, i've spent half a day on 
it with no progress!

Cheers

Jon
[I do not believe that this is a session timeout problem as specified in 
a 5.3.9 ("IMP logs me out for no apparent reason at all"). - I have no 
problems with logouts in any other circumstances]