Blog-Page 404

Hi guys, I have a serious problem. If I open the Blog-page i get a 404 Error. http://bunkerkirche.kopten.de/aktuelles/ I did some research and found similar problems but no solutions. The page is set as Blog-page in the settings (Dashboard>Settings>Reading). If I switch the setting to another page this page gets a 404 error and the other page is accessible again. Sadly I am not Admin so i can't tell you the plugins that are installed -.- Best Regards Anton