Developer 18, lesson 4.

I'm trying to create code from this lesson and I get the following error.
Any ideas?

Run-time error '-2147352567 (80020009)'
You can't assign a value to this object.

Details

Option Compare Database
Option Explicit

Dim db As Database
Dim rs As Recordset

Private Sub Form_Open(Cancel As Integer)
    Set db = CurrentDb
    Set rs = db.OpenRecordset("TBK01aBooks")
    
    rs.MoveFirst
    
    TBK01aBookNo = rs!TBK01aBookNo
    TBK01aBookName = rs!TBK01aBookName
End Sub
Copy

Regards,
Mike Albert