Add metadata to vApp

Does anyone know how to add a metadata object to a vApp? I am not seeing a Set method for the Metadata object class.

Here is the code I am using:

        private static void AddMetadataForvApp(ref Vapp vapp, string NewNetworkName)        {                MetadataEntryType metadataSnapshotEntry = new MetadataEntryType();                metadataSnapshotEntry.Key = "snapshotEnabled";                MetadataBooleanValue snapshotValue = new MetadataBooleanValue();                snapshotValue.Value = true;                MetadataEntryType metadataNetworkEntry = new MetadataEntryType();                metadataNetworkEntry.Key = "uniqueNetworkName";                MetadataStringValue newNetworkNameValue= new MetadataStringValue();                newNetworkNameValue.Value = NewNetworkName;                MetadataDomainTagType metadataDomain = new MetadataDomainTagType();                metadataDomain.Value = "SYSTEM";                metadataDomain.visibility = "READONLY";                metadataSnapshotEntry.Domain = metadataDomain;                metadataNetworkEntry.Domain = metadataDomain;                Metadata vappMetadata = vapp.GetMetadata();                vappMetadata.UpdateTypedMetadataEntry(metadataSnapshotEntry);                vappMetadata.UpdateTypedMetadataEntry(metadataNetworkEntry);        }

I am getting "Data Not Found" returned from the vCloud web service.