When postback, if TextBox's TextMode is Password, it is passed without a value property, so the password box is empty.
Join the following code:
Private void page_load (object sender, system.eventargs e) {password.attributes .add ("value", request ["password"]); // password is the name} of TextBox
Video tutorial: http://www.allenkuo.com/forum/demo/20041011/keeppasswordValue.wmv
