CloneVM_Task throws error "The request refers to an unexpected or unknown type."

Hi,

I trying to Clone a VM, It works perfect when i specify host managed object Reference(MOR) in VirtualMachineRelocateSpec.

http://pubs.vmware.com/vi3/sdk/ReferenceGuide/vim.vm.RelocateSpec.html

When i try with Cluster managed object Reference (MOR) I'm getting this error "The request refers to an unexpected or unknown type."

   // Get clone specifications

  VirtualMachineRelocateSpec relocSpec = new VirtualMachineRelocateSpec();

     relocSpec.datastore = targetDataStore;

     relocSpec.pool = resourcePoolRootRef;

// assgining cluster compute resource pool...

relocSpec.host = hostParentCompResRef;

If i change it to Host it works fine...

relocSpec.host = hostRef;

I don't want to specify particular host, the Cluster is DRS enabled ....

Still I get this error can anyone help...