Hello,
To begin with, we have hidden your mentioned serial/MAC combination for privacy reasons.
Your both mentioned MAC addresses have already been registered to RMS. Since each router has unique MAC address, this is the reason why you cannot register your two devices to RMS.
If you are typing MAC address by hand, please make sure that you are trying to enter correct MAC address. Take note, that from router's "System -> Administration -> RMS" menu you can copy-paste the MAC address to avoid any errors.
If indeed your both devices have exact MAC addresses, which you mentioned before, please download troubleshoot package form both of them and send it to me via private message. Troubleshoot package can be downloaded from "System -> Administration -> Troubleshoot" menu.