Required field validator stopping image button onclick?

Question

I'm having an issue with an image button that I have built. When I attach required field validators to the page, they stop the button onclick event from firing. I am pretty perplexed by this as I can't see any issues in my code!

Please could you cast your eyes over this and help me out?

Cheers

<asp:TextBox ID="TB_Newsletter" runat="server" CssClass="nwsltr-input"></asp:TextBox>

        <asp:RequiredFieldValidator ID="RequiredFieldValidator1"  ValidationGroup="V1" runat="server" Display="Dynamic"  ControlToValidate="TB_Newsletter" ErrorMessage="You must enter your email address"></asp:RequiredFieldValidator>

        <asp:RegularExpressionValidator ID="RegularExpressionValidator1" 
           runat="server" ValidationGroup="V1" Display="Dynamic"
           ValidationExpression="^([0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$" 
           ErrorMessage="Invalid Email Address" ControlToValidate="TB_Newsletter"></asp:RegularExpressionValidator>

      <asp:ImageButton ID="IB_SubScri" 
           ImageUrl="~/_includes/images/buttons/nwsltr-btn.png" runat="server" 
           onclick="IB_SubScri_Click" CausesValidation="True" ValidationGroup="V1"/>

Answer 1

When you press the button it submits the form, but prior to that the field validators are firing by script - the form won't post if validation fails. <asp:Imagebutton /> and <asp:Button /> types allow you to disable validation when they are pressed:

<asp:ImageButton ... CausesValidation="False"/>

From MSDN on the CausesValidation property:

true if the control causes validation to be performed on any controls requiring validation when it receives focus; otherwise, false. The default is true.

See this MSDN reference for more information.

Obviously, we assume here that the validator firing when pressing this button is not required.