Is this related to the fix https://github.com/ManageIQ/manageiq-providers-vmware/pull/78? (Fixed for Bug 1467399)
Are you doing auto placement with a selected DVPortGroup? If that is the case, fix https://github.com/ManageIQ/manageiq-providers-vmware/pull/78 should solve the issue. Would you like to get a hotfix? If that is not what you were doing, please provide the steps to re-produce the issue. Thanks.
*** This bug has been marked as a duplicate of bug 1467399 ***