Hi,

Example of range validator

Here is your textbox control and rangevalidator control

 <asp:TextBox ID="TextBox1" runat="server">          </asp:TextBox>

 <asp:RangeValidator ID="RangeValidator1" runat="server">          </asp:RangeValidator> 

In code behind

RangeValidator1.ControlToValidate = "TextBox1";

RangeValidator1.Type = ValidationDataType.Date;             

RangeValidator1.MinimumValue = DateTime.Now.ToShortDateString();             

RangeValidator1.MaximumValue = DateTime.Now.AddDays(7).ToShortDateString();             

RangeValidator1.ErrorMessage = "Select date between today to next 7 day!";