Check the address book record for the beneficiary to see if their "real name" has been set to a blanked or set to a single character by accident. The "real name" field overrides the "nickname" field. Go to "Estate..Beneficiaries", right click on the beneficiary and select "address book entry" you'll be able to see the entries for "nickname" and "real name".
Also, check that the address book does not have a blank record at the top of the list of addressees. See "Home..Address book".