We are all FC / VMFS shop. Doing full storage migration, evacuating old arrays, filling new arrays. Strictly storage vmotion.
Source datastores are VMFS5. Destination datastores are VMFS6.
My Move-VM scripts worked perfectly for about 3500 VMs which didn't have snapshots. The remaining 500 or so which have snapshots all fail with this same error. Don't ask why we have so many snapshots. It's a sore subject :/.
Manual vMotion works just fine.