List Category Function Error

My wp_list_categories(); function has started outputting this error:

Warning: Parameter 1 to sphoto_list_categories() expected to be a reference, value given in /data/25/1/39/105/1854757/user/2013693/htdocs/blog/wp-includes/plugin.php on line 170

I Googled the error message and it looks like there are lots of other wordpress blogs with the same problem. I did a few whois lookups and was able to throw out the possibility of it being a hosting provider issue. I am running the latest version of WordPress.