1. Add ValidationSummary control and set its ShowMessageBox property to True and ShowSummary property to false.
2. For all validators set Display property to None.
Name: (Required)<br />
<asp:TextBox ID="txtName" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" CssClass="Validators" Display="None"
ControlToValidate="txtName" runat="server" ErrorMessage="Name is required."></asp:RequiredFieldValidator>
<hr />
Email: (Required and Valid Email Address)<br />
<asp:TextBox ID="txtEmail" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredFieldValidator2" CssClass="Validators" Display="None"
ControlToValidate="txtEmail" runat="server" ErrorMessage="Email is required."></asp:RequiredFieldValidator>
<asp:RegularExpressionValidator ID="RegularExpressionValidator6" runat="server" ErrorMessage="Invalid Email Address"
ControlToValidate="txtEmail" CssClass="Validators" Display="None" ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*">
</asp:RegularExpressionValidator>
<hr />
Age: (Required and Range 18 - 45)<br />
<asp:TextBox ID="txtAge" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredFieldValidator3" CssClass="Validators" Display="None"
ControlToValidate="txtAge" runat="server" ErrorMessage="Age is required."></asp:RequiredFieldValidator>
<asp:RangeValidator ID="RangeValidator1" CssClass="Validators" Display="None"
MinimumValue="18" MaximumValue="45" Type="Integer" ControlToValidate="txtAge"
runat="server" ErrorMessage="Age Range 18 to 45"></asp:RangeValidator>
<br />
<br />
<asp:ValidationSummary runat="server" ShowMessageBox="true" ShowSummary="false" />
<asp:Button ID="btnSubmit" runat="server" Text="Submit" />
Screenshot
