c# - Error using Settings file. -

c# - Error using Settings file. -

i'm trying utilize settings file in vs 2013 store text of textbox1.text , re-input when open application again.

i have setup this.

settings file here: http://i.gyazo.com/e3aef293c3b8dbdfab269718de81a310.png

on public form1() have read text.

textbox1.text = properties.settings.default.aaa;

then on saving have this.

if (checkbox1.checked) { properties.settings.default.aaa = textbox1.text; }

but error

'windowsformsapplication1.properties.settings' not contain definition 'aaa' , no extension method 'aaa' accepting first argument of type 'windowsformsapplication1.properties.settings' found (are missing using directive or assembly reference?)

thanks help.

c# settings