Why does code for author listing not work?

I want to add a page with author listing and try to use next code:

<?php wp_list_authors(‘show_fullname=1&optioncount=1&orderby=post_count&order=DESC&number=3’); ?>

as recommended on page:

http://codex.wordpress.org/Template_Tags/wp_list_authors#Source_File

This code gives a blank result in my blog. I use plugin ‘php_execution’ for which I had to uncheck ‘WordPress should correct invalidly nested XHTML automatically’ in “writing” in the admin section before I got simple code (echo “hello world”) at work.

I suppose this was enough to ascertain the good working, so do I have to add some additional code? I changed ‘show_fullname’ from 1 into 0 whithout change (as there are only nicknames).

Anyone any idea what is wrong? Thanks.