Can't figure out why wp_generate_attachment_metadata breaks

I have a chunk of code that sets up an attachment, but it seems to break when setting meta-data, and I can't see anything wrong. Any chance someone could look at the code below and see if anything jumps out as the problem?

dg_debug_log("Setting up attachment assignment for thumbnail.");
// set up the attachment assignment for the thumbnail
$attachment_id = wp_insert_attachment($attachment, $new_file, $post_id);
dg_debug_log("wp_insert_attachment completed");
if($attachment_id != 0) {
dg_debug_log("Inside attachment if statement");
dg_debug_log(" new_file: " . $new_file);
$attachment_data = wp_generate_attachment_metadata($attachment_id, $new_file);
dg_debug_log("attachment metadata generated.");
wp_update_attachment_metadata($attachment_id, $attachment_data);
dg_debug_log("attachment metadata updated.");
update_post_meta($post_id, '_thumbnail_id', $attachment_id);
dg_debug_log("post meta updated.");

The thing is, since the log shows making it inside the if, the id should be good, and since the file name seems okay, the new_file variable should be good. So I don't understand why the program simply stops executing at wp_generate_attachment_metadata.

Here's the debug dump:

Setting up attachment assignment for thumbnail.
wp_insert_attachment completed
Inside attachment if statement
new_file: /var/www/zdecade/wp-content/blogs.dir/2/files/2012/01/Rainer Ebert.jpg

Ideas would be appreciated greatly.