Question : Access 2007 calculated field

I would like to add a text field that gets assigned a value "No records" if there are zero detail records and blank (no text) if there are records.  I experimented with an IIF in the ControlSource of the textbox, but I get an error.

I an doing this on a test database.  The master table (Test-Master) has one numeric field called "Key".  The detail table (Test-Detail) has two numeric fields ("Key" and "Data").

I successfully counted the detail records by a calculated field  "Count(*)"  in the "Key Header" section

Any ideas would be appreciated

Answer : Access 2007 calculated field

Assuming the textbox is named MyTextbox, Place in the form's on current event:
Private Sub Form_Current()
if Me.Recordset.RecordCount = 0 Then MyTextbox = "No records"
End Sub