>When user changes textbox in form, the textbox class performs a refresh of a navigation grid. In the refresh method of that grid I set this.enabled = .F., but the grid doesn't become disabled! Specifically, the user can still click on another row (precisely the kind of behavior I wish to avoid).

Not sure exactly what your problem is, but one old technique for grids is to cover/uncover them with a transparent grid-sized Shape - when you don't want users accessing them *at all*. Just an idea if other solutions cannot be found...and not too hard to implement.