I see you insisted to put it in a change event. My textbox is linked with a cell in which you have the formula : =today(). User won't change it.
I trew to do what you said but if I changed the system date to update the content of the result =today(), the textbox is not being updated. Indeed, the textbox must be updated automatically when the date is changing.
Please, do you have another solution that will really work in this case ?
Insert a TextBox from the Drawing Toolbar. Select it, go to the formula bar, type =, point at the cell you want to link to and press Enter. When you select the TextBox you should see a formula like =$A$1 in the formula bar.