Did you try looking up your license, on the SmarterTools website, and re-applying the license in the old version?
When you downgraded, did you completely UNINSTALL SmarterMail 13.X, REBOOT, and then do the installation for SmarterMail 12.X?
Phone: (224) 444-0169
E-Mail and DNS Security Specialist
Network Security Specialist
Customer Service Portal: https://portal.chicagonettech.com
Security Blog: http://networkbastion.blogspot.com/
Web and E-Mail Hosting, E-Mail Security and Consulting