unexpected T_CONSTANT_ENCAPSED_STRING

I am having a problem with the following code. The problem appears to be line 507 which is the one that begins with $output. I’ve been going round and round here. I’m trying to link to the current page, but I’m new to php. Please help. I’m feeling so lost here. The error is:
Parse error: syntax error, unexpected T_CONSTANT_ENCAPSED_STRING in /hermes/waloraweb016/b122/as.setoncenter/home/wp-content/themes/priimo/functions.php on line 507

if(has_post_thumbnail($entry['id'])) {
            $img = get_the_post_thumbnail($entry['id'],'priimo-slide-image');
        } else $img = '<img class="priimo-default-slide" src="'.get_template_directory_uri().'/images/default_slide_image.png"/>';
	$output .= '<a href='http://www.setoncenterinc.org'></a>'."\n";
    }
    if(trim($output) != '') {
	$slideshow .= '<div id="coin-slider">'."\n";
        $slideshow .= $output;
        $slideshow .= '</div>'."\n";
    }
    echo $slideshow;
}