For GUEST registered systems, get_email_contacts() fails.
The system_identifier passed to get_email_contacts is "converted" to a MAC address. This conversion fails if the given time stamp is the time stamp of the guest registration. This failure is due to the fact that the DHCP lease is granted after the guest registration is accepted.
The fix is to notice if the given system_identifier is already a MAC address. If so, then the "conversion" is skipped.