It's difficult to get the plugin to throw an error on the cron event though because it's an event that's supposed to fire without specific user intervention and as such the should not be an expectation of direct user feedback.
In the current code there are 3 messages that a user may see in respect of the cron event. If digest is enable and Preview is clicked it will report 'Preview message(s) sent to logged in user'. If an attempt is made to resend a digest it will either report 'The Digest Notification email contained no post information. No email was sent' if there was no data to send or 'Attempt made to resend the Digest Notification email'.
How would you suggest that the usability is improved above this?
Try installing WP-Crontrol to see if cron events are scheduled and working. Also ask your host if they have disabled it.
If you want to use a 'real' cron task to get these working see my first reply in this thread.
Also, please not for future reference, it is considered good practice to open a new thread on a forum if you are asking a new question. Only reply to threads if you are adding information in the exact same scenario or have suggestions on a fix.