Error: "Unable to connect server" when connecting XenCenter to a Pool Master

Cannot connect to Pool Master by using XenCenter. XenCenter gives anerror message: Unable to connect to server '10.90.206.83'. Could not find XenServer on '10.90.206.83'. Check that XenServer is configured correctly on '10.90.206.83 and try again. However, Pool Master is accessible by SSH. The...