Simple Tags Plugin for Wordpress 2.9
Open the simple-tags.php file.
Look for the following code (It's near the top):
if ( strpos($wp_version, '2.7') !== false || strpos($wp_version, '2.8') !== false) {
and replace it with:
if ( strpos($wp_version, '2.7') !== false || strpos($wp_version, '2.8') !== false || strpos($wp_version, '2.9') !== false ) {
Bob's your uncle.