What's wrong with these two lines of code?

$options = array('attributes' => array('class' => 'sidebarmore') );
$output .= '<br />' . l('More ' . $category_name . ' >>', 'node/281/', null, 'tid=' . $tid, $options);

output:

<a href="/node/281/?tid=58#Array">More Travel >></a>

Why doesn't the class attribute show up in the output?