vCenter 6.x: Unable to deploy template

I had a VM on vSphere 5.5 that I was trying to move to a new ESXi 6.7 host via vCenter.

First I exported the OVF template from vSphere 5.5.

Then in vCenter, on the vSphere 6.7 host, I deployed the OVF template.

Error!

The "Deploy OVF template" operation failed for the entity with the following error message.

Unable to deploy template.

The error was vague. Why was it unable to deploy the template? Is there a compatibility issue between 5.5 and 6.7?
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