[imp] Premature end of script headers: /kunden/74076_81677//horde/imp/folders.php

[Umbroboy]

Hello,

when i would like to see the folders in imp and click on the folders button 
i get an error message 500.
The CGI-Debugger shows me this error:

Premature end of script headers: /kunden/74076_81677//horde/imp/folders.php


This is my IMP Version: H3 (4.0.2)

Has anybody an idea?

Thanks umbroboy