Fatal Error… please help!!

I changed the theme on our wordpress site and am now getting this fatal error when I try to load the site as a visitor, as admin and even through our host. We have done an enormous amount of work on it and I am in panic mode. Please help me!!
Fatal error: Can’t use function return value in write context in /home/content/p3pnexwpnas01_data03/39/3221939/html/wp-content/themes/voltata/inc/template-tags.php on line 174