Subject Cannot edit current row error

I am writing my first app using IBO and IB after years of BDE and

I have a screen with an IB_Grid and IB_Query displaying records and
New and Edit buttons. The New button appends a new record and
displays an input screen with IB_Edit fields. This works fine and I
can add or cancel records.
The Edit button is supposed to put the dataset into edit mode
(IB_Query.Edit) and display the input screen for editing of the
selected record. However, when IB_Query.Edit is executed I get
a 'Cannot edit the current row' error message. The input/edit screen
displays the fields of the selected record but you cannot edit the
data. What am I doing wrong?

I would appreciate it if anyone had any suggestions.