why am I getting error 321 here

Question

If Not (Me.frmBookDetailsSub.Form.Recordset.EOF And Me.frmBookDetailsSub.Form.Recordset.BOF) Then

    If MsgBox("Are you sure to delete?", vbYesNo) = vbYes Then

'delete row

    CurrentDb.Execute "DELETE FROM tblBookDetails " & _

    "WHERE BookDetailsID=" & Me.frmBookDetailsSub.Form.Recordset.Fields("bookdetailsid")

    'refresh data in sub form

    Me.frmBookDetailsSub.Form.Requery