Due to changes in VMware vSphere on single host setups, it is not possible to import certain OVA images if they use compressed disks, as is the case with the new Platform-9.1.ova image. To get around this, you can use the ovftool from VMware to import the OVA successfully.
Importing OVA with ovftool
The example below is for Windows, but the ovftool is available for Windows, Linux and macOS in 32-bit and 64-bit flavors.
The network is selected with the --net: switch, which selects the "nat" network that the ovf expects/requires and the "VM Network" that exists on Hypervisor.
Next, point to the download.
Specify the host and VMware user that you are using to deploy the OVA.
The output should resemble this:
Opening OVA source: I:\Downloads\Platform-9.1-20180622.ova
The manifest validates
Opening VI target: vi://firstname.lastname@example.org:443/
Deploying to VI: vi://email@example.com:443/
PS C:\Program Files\VMware\VMware OVF Tool>
This is a simple setup; yours could be more complicated, depending on your vSphere deployment.