When enrolling a certificate through Entrust.net, an error at stage 500 is given stating that you have too many SANS in the request.
This error is a response from Entrust, they have SAN limitations on the products that can be selected. To be able to request certs through Entrust that have 1 SAN, the "Standard" Template can be used. With only 2 SANs the "Advantage" Template can be used. For more than 2 SANS the "UC Multi-Domain" Template should be used.
To select a different Entrust Template, navigate to the Entrust CA Template in the Policy Tree in WebAdmin.