<asp:TextBox ID="TextBox1" Runat="server">My Initial Value</asp:TextBox>&nbsp; 

<asp:RequiredFieldValidator ID="RequiredFieldValidator1" Runat="server"  
 Text="Please change value" ControlToValidate="TextBox1" 
 InitialValue="My Initial Value"></asp:RequiredFieldValidator>

<asp:RequiredFieldValidator ID="RequiredFieldValidator2" Runat="server" 
 Text="Do not leave empty" ControlToValidate="TextBox1"> 
</asp:RequiredFieldValidator>
