Why virt-v2v fails to connect to vsphere 6.0 with error "Permission to perform this operation was denied." for non-administrator user?

Issue

• While trying to convert a virtual machine form vsphere 6.0 environment, the user has all the documented roles assigned. Using this user, it is possible to log in to vsphere GUI and can browse the needed datastores, clusters and hypervisors successfully.
• The virsh comand succeeds with an full Administrator account.
• What roles are required for a non-administrator user to successfully convert vms form existing vsphere environment.

error: failed to connect to the hypervisor
error: internal error: HTTP response code 500 for call to 'SessionIsActive'. Fault: ServerFaultCode - Permission to perform this operation was denied.