[R8000] Can not add IP to Address reservation table

[piapia24]

Dears, 

I just try to add my device to "Address Reservation Table" and I have an error:

I already add some devices, and last one is 192.168.88.162:

I would like to add next one: 192.168.88.165 or 192.168.88.161 and I have got an Error 400.

What I have to check more?

ps.R8000 firmware is upgraded.

thx for support