Welcome to the Community,
this error message usually appears if the source machine (Windows 2008) cannot resolve the ESXi host's FQDN name. Unless you have a DNS server in place, you may add an entry for the ESXi host to the Windows 2008 server's hosts file (e.g. <IP address> <ESXi hostname> <ESXi FQDN>, sample: 192.168.1.11 esxi01 esxi01.domain.local).
André
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