I've have had very little success in general uploading OVA templates using the ESXi host client. On 6.0 you can still use the C# client. Uploading via vCenter also works. I haven't tried it on 6.5 yet.
Uploading via the OVFTool command line utility does work. The issue you have when you do a push is it tends to create it with a newer vmx version (virtual hardware version) which makes the boot loader environment innaccessible. You can work around this by adding a floppy drive to the VM and attaching a blank floppy image.
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Thanks for the tip about the vmx version - I didn't need the to add the floppy because, the vCenter Standalone Converter has an option for Hardware Compatibilty "Virtual Machine Version - dropdown" before you push it up. - I had been choosing the newest version before.
NOTES - For anyone needing help with this issue (Also see attached images):
I opened the ova in VMware Workstation v.12 -Saw that it defaulted to a version 6.5-7x virtual machine when I chose manage -> change hardware compatibility - see image
Then I used Stand Alone Coverter - chose Convert Machine option - and navigated to the Workstation's VM folder (You need the vmx which is why I opened it in Workstation) - to push it up to my ESXi 6.5 host.
Before I pushed it, I made sure to select version 7 from the Virtual Machine Version dropdown.
The Simulator image comes with 4 Drives attached and they're all THICK provisioned.
One of those drives is 230GB - So you might have to set it to thin provisioned based on your environment - because your host storage may not have room for all 230GB to be thick provisioned.
Again - The standalone converter gives you the option to edit the VM's parameters before pushing it up so you can switch.
Sean was right about the VM Hardware Compatibility issue but, I didn't need the "Virtual Floppy" because, the vCenter Standalone Converter has a Hardware Version/Compatibility drop down option before you push.
I opened the OVA in Workstation - then pointed the standalone converter at the vmx file.
I chose version 7 (Workstation showed it as 6.5-7x compatible once opened) before I pushed the VM up to my ESXi 6.5 host.
The simulator comes with 4 Drives attached - DEFAULT TO THICK PROVISIONED IN STANDALONE CONVERTER - one of which is 230GB - so you may have to change to thin provisioned.
Again the standalone converter gives you this option.