[Zope] problem downloading PDF:File does not begin with '%PDF-

Hi there, for some time (10 days) we have problems downloading PDF-Files from a zope site. It used to work before. The only thing that was done, was updating Linux with security updates. Now we get on windows clients:File does not begin with '%PDF-' (both with IE6.x, Firebird, Mozilla). On a Linux client things work fine. When I change the content-type in the ZMI from application/pdf to application/x-pdf The file is downloaded and presented in the acrobat reader without glitch. What we use is: Zope 2.7 Python 2.3.3 Apache 2 Suse Linux 9.1 (Kernal 2.6) Can somebody indicate me towards an solution less radical than changing all content-types ? Thanks Robert