With hosts prior to ESXi 5.1 involved, you can only storage vMotion if all hosts have the storage presented. Before you present the old storage to the new host, ensure the storage is supported by ESXi 5.1! If this isn't the case you may need to present a LUN from the new storage system to the 4.1 host(s) and create a "transfer" VMFS3 datastore.
André
