By default, all domain Admins are members of vCenter Administrators but this is not enough for HP Plug-in. You can solve it by adding your account explicitly on the highest level of your infrastructure.
You also can access the plug-in setup by using the local administrator of your vCenter Server which is not recommended
On the prerequistites side, you need to create master accounts for iLO, Virtual Connect, ESX and VMs (optional).
Regards,
Ahmed