Update a payment draft

Hi,

I'm using the following code in order to update the cardname of a payment draft:

di.Payments diPayDraft = DiCompany.GetBusinessObject(di.BoObjectTypes.oPaymentsDrafts) as di.Payments;

       diPayDraft .GetByKey(Convert.ToInt32(DiCompany.GetNewObjectKey()));

       diPayDraft .CardName = "TEST";

       diPayDraft.Update();

The update returns with 0, which means that it is completed successfully but the cardname stays the same and doesn't change to "TEST".

Any idea what is wrong here?

Thanks,

Ori.