503 ever since new Theme

Hi,
Ever since I changed the theme of my site I get plenty of 503 errors that look like this:

wp-login.php?action=lostpassword&redirect_to=http://darumbinichblank.de/macbook-schutzhuelle-aus-echtem-holz/

I have no idea if it comes from a plugin I installed that interfers with the theme or what the problem might be. I would be very pleased if someone could help me with that….My page is http://darumbinichblank.de/

Thank you very much