>I cannot remember how...
>In the development environment I am editing a grid class. (It has one column)
>I drag another control to place in the column and I get the error :Cannot add this object to Grid.
>I am dragging a control from my base classes to the grid column.
>It doesn't matter which one.
>
>I've tried two things.
>1. Just select the grid.
>2. Select Column First and then drag to grid.
>
>What am I forgetting?

In PEM window, select the column. Then drop a control.