Hi - to prevent user input on textboxes try the following:
Add an imagebutton to you page(after the textbox):
<asp:ImageButton ID="ibtnDOB" runat="server" ImageUrl="~/Images/btncalendar.png" Height="25" Width="23" AlternateText="Select A Date" />
Modify your Calendar control to use the image button:
<asp:CalendarExtender ID="ceDOB" runat="server" Format="dd-MM-yyyy" TargetControlID="txtDOB"
PopupButtonID="ibtnDOB" ClearTime="true" />
Change your textbox to:
<asp:Textbox ID="txtDOB" runat="server" cssclass="cntls txt txt-calender" maxlength="10" AutoComplete="off" placeholder="dd-MM-yyyy" onfocus="this.blur();"></asp:Textbox>
Hope it helps.