If you’re using timthumb in your wordpress theme on WordPressMU and it’s not finding certain files, this may be why:
WordPressMU uses the blogs.dir directory to store uploads. timthumb’s search routine when looking for images to resize doesn’t include this directory.
Here a modified version I created that does include the dir:
You will need to add the following query param to all your timthumb.php URL’s when using this version:
blogid=<?php echo get_current_blog_id(); ?>
That way timthumb knows which blogs.dir directory to look in for images.