Classifieds plugin Error : Call-time pass-by-reference has been removed

I have the Classifieds plugin installed at classifieds.thedirtdivas.com and now I notice an error:
Fatal error: Call-time pass-by-reference has been removed in /home1/dirtdiva/classifieds/wp-content/plugins/classifieds/custompress/core/content-types.php on line 616

How do I fix this?

Thanks!