Note that the email address entered is the one that you use to log in to the software. So don't blank it out - you won't be able to get back in. And you will make it difficult for yourself if you put something like 'firstname.lastname@example.org / email@example.com'.
A further thought. If you've entered a sold date or amount against the address, then the system considers the property sold and won't generate further rents. That's a common reason for this situation.
There are a number of reasons the software won't create rents. I wrote a blog post which discusses some of this, and generated some user comments about problems people have.
I can check your account if you email me just the login email account you used. My email is...