Seeking within the archive failed (VERR_TAR_UNEXPECTED_EOS).
Result Code:
VBOX_E_IPRT_ERROR (0x80BB0005)
Component:
ApplianceWrap
Interface:
IAppliance {8398f026-4add-4474-5bc3-2f9f2140b23e}
Actually, a friend contacted me today asking about this issue as he was unable to get Dietpi running in his Virtualbox, so I thought I'd give it a whirl and have the same experience.
Other OVA's import fine on my machine, including a new VB install in a new OS I've never used before, so I don't *think* it's me.... but it could be!

Regards
Christian