Hy everybody and hello from germany. We are running

Hy everybody and hello from germany. We are running in trouble. All frontpages from our MU(Subfolder) are not working. All other links like http://www.site1.com/page are working but if you want to go on site1.com and set in settings/reading static front page the page stay white.

htaccess is default from MU and we are running wordpress 3.7.

Thanks for help.