Using ValidatorCalloutExtender to Enhance RequiredFieldValidator to validate.

Step 1 : First you require Ajaxtoolkit to be added to your  asp.net toolbox.

Step 2: 
Add the RequiredFieldValidator control from toolbox for textbox control to validate.

Step 3: 
Add the ToolkitScriptManager control from the toolbox just below the form tag.

Step 4:
Use the ValidatorCalloutExtender control from the ajax toolkit tools which you have got after adding ajaxtoolkit.dll to the toolbox.


The code must look like this :

<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">

</asp:ToolkitScriptManager>

<span> First Name</span>

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

<asp:RequiredFieldValidator ID="rqdFirst" runat="server" ControlToValidate="txtFirstName" ErrorMessage="Enter First name!" Display="None"></asp:RequiredFieldValidator>

<asp:ValidatorCalloutExtender ID="ValidatorCalloutExtender1" runat="server" TargetControlID="rqdFirst">

</asp:ValidatorCalloutExtender>

The output window will look like this :