"POST made from IP out of range" error was returned by script when tried to send a POST to server

[babadook]

Hi,
a third party billing provider (CCbill) is getting this error "POST made from IP out of range" while trying to send command to their script on my server.
I have whitelisted their IP ranges but still running into this problem. Searching forum didn't help.
Anyone knows what this could be nd how to fix it?
Thanks.