Vmware Backup Proxy OVF deployment fails with the following errors:
Transfer failed: The OVF descriptor is not available.
Transfer failed: IO error during transfer of 'null': null
This issue is experienced when you try to deploy the OVF template using the web client on a Vcenter server prior to version 6.7 Update 1.
Deploy the OVF using a different browser. (e.g IE to chrome).
According to Vmware, this issue is fixed in vCenter Server 6.7 Update 1.