Why a textbox.ControlSource do not accept an expression like a Column.ControlSource.

Expl. ‘table1.prise1 – table1.prise2’ or ‘UPPER(table1.name)’ is accepted in a column.ControlSource bat not with a textbox.ControlSource.

When I try this with a textbox.ControlSource the ERROR 1742 occur.
Maybe somebody encountered the same problem and now why textbox.ControlSource do not accept this and has a solution for this problem.

Tanks