Even though your server can be ping'd, UD could not resolve those two server names to IP addresses. Did you ping by server name or IP address?
As you found out, you can use either the server name or the IP address in UD. The situation you were in was probably you doing an edit to the config file to get UD to "think" it had resolved the server name. That used to work, but I've been working through a lot of issues with UD that caused problems with character sets that make php fail. The Chinese character set has been particularly challenging. That's why the situation you had failed after a UD update.