Unfortunately, this "Protecting Send Service" message indicates an internal fault on the KD-R660. The unit needs to be opened and JVC recommends that the receiver be sent to a service center.
I wish that I had better news for you. The trouble-shooting information for the error is given on page 21 of the manual. The manual is available here: https://www.carid.com/images/jvc/stereos/pdf/kdr460-guide.pdf .
Cindy Wells