I have the exact same issue.....  I reported this over on the Re: Cannot export to OVA after Upgrade to 6.5 thread, as I, unfortunately, found that thread before I found this one, but the end result is exactly the same as you stated....  My only difference is the host machine I am using is an HP Proliant DL360 Gen 9 server.  I should also state I'm not trying to export a Linux distribution, either, but rather, they're all Windows OS platforms.....  Varying types (i.e., Windows Server 2016, Windows 10 and Windows 7 during today's attempts).

I had read (elsewhere) that OVF Tool could be leveraged to accomplish the task-at-hand, which bothers me greatly--never having used that tool before....  Looks like I need to get acquainted with it, since I don't see/hear anything which makes me believe a fix for this in the Web GUI is in the offing anytime soon....  I dislike having to resort to this, as I see the issue at-hand as a defect in the current GUI, and I shouldn't have to download a different tool, learn how to use it, (and deal with outputs different from what I am accustomed to).  I mean, I guess I am 'glad' such a 'workaround' exists (it could be worse and no workaround exists), but I would like to believe something is actively being done on this particular matter--and is getting solved rather than relegating it to the back burner simply because a "workaround" exists.....

Now I have to take time out of schedule and try to get savvy enough to use OVF Tool.....

I suppose I could look at this a yet another learning experience--and making myself all the more marketable by not being stymied when hitting one brick wall--turning 90 degrees and running smack dab into another brick wall....  What quirks will I encounter with OVF Tool, I wonder....

Would be very nice to hear from someone in authority that this matter (along with the other "quirks" I mentioned on that other thread) are actively being addressed.

Best Regards,