There is a function call to uc_order_admin_comments in uc_file.ca.inc in the "Renew Files" Conditional Action using an undefined variable on Line 262.
Here's the call:
uc_order_comment_save($order->order_id, $user->uid, $comment);
Problem is the $user variable is undefined. I'm not sure if this is supposed to be the global $user or $order_user, but it needs to be something other than 0.
To test this is in fact a bug, you can run a simple query:
SELECT uid FROM uc_order_admin_comments WHERE message LIKE '%User can now%' LIMIT 10;
You should get all 0's