Brower keeps refreshing on site with JavaScript

Hi,
We have the problem, that a Site with a JavaScript will be refreshed and
never shown completly when browsing over the Proxy Server. But on the
ContentFilter, no Filters are active beside Virus Scan. Also, the requested
Site is on the Whitelist - without the Proxy it works fine.
Here is the Site: [url]http://www.egl.ch/int/ch/de/markt/swep/aktuell.4.html[/url]
Running NSM/Astaro 6.303.
Thanks in Advance for any tips and help.
Regards,
Daniel