Problem with SetBound (or Bind) on SAP B1 Built-in field

Hi,

I'm trying to add an EditText to the Sales Order form and bind it to ORDR.NumAtCard.

Whenever I do the SetBound or Bind it fails with "Exception from HRESULT: 0xFFFFFBF7"

Code is:

Dim itm As Item

Dim et As EditText

itm = form.Items.Add("txtNA", BoFormItemTypes.it_EDIT)

et = itm.Specific

et.DataBind.SetBound(True, "ORDR", "NumAtCard")

If I use a UDF rather than NumAtCard it works fine.

Any ideas what is wrong?

I am wondering if it's impossible to bind an EditText I added in code to a built in B1 field...