For some unknown reason, a few of the IPs on one of my machines are unreachable. I have made no changes to the server in the last few days. Could my NOC have given someone else the same IPs? This is a huge problem as many clients cannot access their site. Does anyone know about this?

Thanks in advance.

Have you tried chaning the IP for one of the sites and than reassigning the same IP to that site? That happened to me once and I had to just reassign the IP back to the site and it started working.