I'd just start by looking at the available net pools from the Provider vs that this OvDC is in. Then see if it's connectable if you were to place a VM/host into it.
I think it'll be somewhere along the lines of the Distributed Switch or NSX isn't spanned to one or some ESXi hosts in the resource pool/provider.
It's been a long time since I've seen this ... and don't work at VMware any more to dig deeper than my memory serves (stupid page faults).
If it's a new message ... was anything changed recently? (resources added/changed)