Normally a readonly textbox (where ReadOnly=true) cannot be edited. Use the ReadOnlyAllowsEdits property to enable editing by the popup Calendar and commands, such as those shown in the Help button, context menu and keystroke shortcuts.
Put the focus in the textbox and use commands like up and down arrow. Click on the Help button or popup the calendar to further change the value. Try to type a date and it will not be allowed.<br/><br/> <des:DateTextBox ID="DateTextBox1" runat="server" ReadOnly="True" ReadOnlyAllowsEdits="True"> <HelpCommandAndButton ShowButton="true" /> </des:DateTextBox>