[imp] Empty window when opening mail

[Muenz, Michael]

Dear List,

I've got a strange problem. My server hosts over 200 accounts
perfectly. Users accessing with POP3, IMAP and IMP. No 
problem so far, but today one user gets mail with 17 attachments.
When he check the link an empty window opens. I can open
the mail with Thunderbird without any problems. Nothing in the
configuration has changed and nothing to see in the logs. I have 
also dumped the complete IMAP connection and saw that all
attachments were serverd from the server and IMP sended a
regualar logout when loading the empty window was finished. 
I'm using: PHP 5.1.2, Apache 2.0.55, Horde 3.0.9, IMP 4.0.4
and Cyrus 2.3.1. I've also tested with a 3.0.7 setup, forwarding
 the mail to my own (as text and attachment), everytime the 
window is empty. 
I guess it has something to do with the encoding.
Any ideas?
Thanks,

Michael