White and freezing Site after Download something

Hi there,
i’ve a question about the WP-Downloadmanager.

I installed it and upload some media files to download. If I download a File now, I get the download, but also a freezing Site.
I can’t click anything, it look like it hang up. I have to reload the site to navigate again.

It’s this site:

http://anonym.es/?http://www.jsv-quetsch.de

I would be happy if someone can help me in this case.

Thank you in advance and best regards
Manuel