ASP.Net AJAX WaterMarkExtender not working

I have used your code and it’s working. Probably you have not registered your AjaxControlToolkit properly.

 Register it like this.

<%@ Register TagPrefix="cc1" Namespace="AjaxControlToolkit" Assembly="AjaxControlToolkit" %>

Check intelligence is coming or not when you start typing

<cc1:

Or you can use Placeholder like this instead of using Water Mark Extender

Like this.

<asp:TextBox ID="txtName" runat="server" placeholder="Enter Your Name"/>

With PlaceHolder and WaterMarkExtender

<asp:TextBox ID="TextBox1" runat="server" AutoPostBack="true" OnTextChanged="Charges_click"></asp:TextBox>
        <cc1:TextBoxWatermarkExtender ID="TextBox1_TextBoxWatermarkExtender" runat="server"
            Enabled="True" WatermarkCssClass="watermarked" TargetControlID="TextBox1" WatermarkText="Charges per day">
        </cc1:TextBoxWatermarkExtender>
        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
        <cc1:TextBoxWatermarkExtender ID="TextBox2_TextBoxWatermarkExtender" WatermarkText="TDS"
            WatermarkCssClass="watermarked" runat="server" Enabled="True" TargetControlID="TextBox2">
        </cc1:TextBoxWatermarkExtender>
        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>
        <cc1:TextBoxWatermarkExtender ID="TextBox3_TextBoxWatermarkExtender" runat="server"
            WatermarkCssClass="watermarked" WatermarkText="Service tax" Enabled="True" TargetControlID="TextBox3">
        </cc1:TextBoxWatermarkExtender>

        <asp:TextBox ID="txtName" runat="server" placeholder="Enter Your Name"/>

Screenshot