This almost always is a problem with DNS settings. Make sure all of your servers have the correct IP settings. Especially DNS. A great way to test this is by pinging the root server by IP address. If you get a positive return, then the IP addresses are correct. Next, you will want to test name resolution by pinging the server FQDN. If you get a negative response, check your preferred dns server address in your NIC settings. If you find that they are correct, and still cannot ping by FQDN, flush the dns cache on the server you are trying to upgrade. Next, reregister the dns cache and try to ping as well. Then reboot. I find that this usually works. You must be able to resolve those names for this to work. If still unable to resolve, try adding a record manually for the server in the dns database. If none of this works, I fear you may have deeper issues to deal with and one (out of many possibilities) being an FSMO role not doing its job.
Best of Luck.
Norm