Error NaN/Nan in urbackup server interface for some PC


I installed urbackup clients in many computers.

Some computer succeeded to connect to urbackup server. And other not.
I don’t why ? they only appear in urabckup server interface when I ciick on show
clients button.

The error message for these computer is Nan/Nan for their Ip their status in the urbackup server interface.
For your information, I disabled the firewall in all computers. The same antivirus is alled on all the computers.

I met the same problem with other computer in an another location.

What is the problem and how to resolve it ?