When you say "... we ...", does that mean you see the same issue for multiple users on different PCs? In this case you may want to check whether any Antivirus/Internet Security/Endpoint Protection or Firewall application causes this issue.
If it's a single PC run ipconfig /flushdns (with the vSphere Client closed) to see whether this helps. Btw. are you able to access the VM's console using the vSphere Web Client?
André