contact us - blank page when sending

Hi guys,
It seems that I've ran into an issue with the contact us form on my web, which I didn't really change. After pressing the continue button i get a blank white page, with no error in the log files and no mail sent.

Using OC 1.5.5.1 with a theme. you can see it here: www.gamers-outlet.net
Anyone has an idea whats wrong here and can help me out?

Thanks.

Hi,
You need see this "www.gamers-outlet.net/index.php?route=i ... ct/success" after pressing the continue button for all correct
I think is problem prettyURL, revise SEO extension that you use.

Bye!