Popup Ajax causing 404 for admin-ajax.php

Trying to enable a popup on this page:
http://utah.pressplayrealty.com/homes-for-sale-results/?zip0=84107&location=&propertyType=SFR%2CCND&status=active&minListPrice=300%2C000&maxListPrice=499%2C999&squareFeet=&bedrooms=0&bathCount=0&_openHomesOnlyYn=on&_dateRange=on&reg

But keeps throwing an ajax error saying admin-ajax.php is missing. It isn't. If you remove the query string you get a result. Something wrong here.