Error, help! Warning: array_key_exists()

I have the same error. Pleace help:

Warning: array_key_exists() [function.array-key-exists]: The first argument should be either a string or an integer in ..../wp-content/plugins/display-name-author-permalink/display-name-author-permalink.php on line 55

What cam we do???

Ok, i dont no, but i have make this:

In the display-name-author-permalink.php
Search:

// Replace the username in author links generated in the theme with the users display name
	function filter_author($link,$author_id,$author_nicename) {

        	if ( array_key_exists($author_nicename, $this->users) )
	                $link = str_replace($author_nicename,$this->users[$author_nicename], $link);
	        return $link;
	}

replace with

// Replace the username in author links generated in the theme with the users display name
	function filter_author($link,$author_id,$author_nicename) {
	if(is_string($author_nicename)) {
        	if ( array_key_exists($author_nicename, $this->users) )
	                $link = str_replace($author_nicename,$this->users[$author_nicename], $link);
	        return $link;
	}
	}

I have this snippet just found. I do not know whether that’s right or what happened to it. The error is no longer displayed.
Important: I do not guarantee.

Dear Support Team. Please tell me how to fix this error! If the code is ok, then you say please.