nullmailer - Sending failed: Could not exec program

[compdoc]

> I've installed nullmailer and configured (or misconfigured) it. However, 
>I am not receiving mails and sudo nullmailer-send brings up the following:

If there are messages stuck in the queue because of misconfiguration, it
will never send any of them. 

The queue is located:

/var/spool/nullmailer/queue

But you have to be root to enter that folder, so first type:   sudo su