Hi,
Just as b0rbb mentioned, your best bet is to get vCloud Networking & Security 5.1.2. I have documented this problem and resolution at my blog including a link to where you can get the just released vCNS 5.1.2 and release notes at: vCloud Networking & Security 5.1.1 create dvPort Groups, but fails to create vmknic interfaces
Please start using vCloud Networking & Security 5.1.2 for any future implementation, & upgrade your current one.
Regards,
Eiad Al-Aqqad