Why can't a renewal period be 0 years?

I have a 2008 R2 root CA and a 2008 R2 Intermediate CA.

I have created a custom template and assigned the Renewal period to be 0 years.  When I try to enroll a certificate for the Intermediate CA, the request fails.  However, I have noticed that when I set the Renewal period to anything other than 0, the enrollment works.  Is there a reason for this?