As mentioned before, I mentioned vSphere 5.1 currently not compatible with any VMware View version. As of yesterday, VMware has finally released a patch (ESXi510-201210001) to correct the incompatibility issues.
Alternatively you can also download an updated ESXi 5.0 ISO. To download the ISO:
- Navigate to the vSphere Download Center.
- Click View Download for the VMware ESXi 5.1.0 Installable for your version of ESXi.
- On the Product Downloads tab, download VMware-VMvisor-Installer-201210001-838463.x86_64.iso.