asp.net, requiredfieldvalidator disabling events on code behind - asp.net

Question

I'm using Visual Studio 2010 with framework 3.5 and Ajax Control Toolkit .NET 3.5.
I working on a asp.net web forms website.
On a form I have this: a textbox, an imagebutton, a button, a calendar and a requiredfieldvalidator:
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<p>
<br />
<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
</asp:ToolkitScriptManager>
<asp:Label id="Label3" runat="server">Date</asp:Label>
<asp:textbox id="txtInitialDate" runat="server" Width="75px" MaxLength="10"></asp:textbox>
<asp:ImageButton ID="imgBegin"
ImageUrl="~/images/Icon1.jpeg" runat="server"
AlternateText="" Height="24px" Width="24px" />
<asp:CalendarExtender ID="CalendarExtender1" runat="server"
TargetControlID="txtInitialDate"
PopupPosition="BottomLeft" PopupButtonID="imgBegin"
>
</asp:CalendarExtender>
<asp:requiredfieldvalidator id="RequiredFieldValidator1" runat="server" ErrorMessage="*" ControlToValidate="txtInitialDate"
Display="Dynamic"></asp:requiredfieldvalidator>
<asp:button id="Button2" runat="server" Text="Send" onclick="Button2_Click"></asp:button>
</asp:Content>
code behind:
override protected void OnInit(EventArgs e)
{
Button2.Attributes.Add("onclick", "javascript:" + Button2.ClientID + ".disabled=true;" + "javascript:" + Button2.ClientID + ".value='Processing.';" + this.GetPostBackEventReference(Button2) + ";");
base.OnInit(e);
}
protected void Button2_Click(object sender, EventArgs e)
{
string a = "some_value";
}
The interaction here is that the user clicks on the ImageButton, the calendar shows, the user clicks on a date and then hits the button.
The problem:
If I run the website and click on the ImageButton first and pick a date, then when the button is clicked no events are fired.
But if I comment the code of the validator:
<asp:requiredfieldvalidator id="RequiredFieldValidator1" runat="server" ErrorMessage="*" ControlToValidate="txtInitialDate"
Display="Dynamic"></asp:requiredfieldvalidator>
Then the events are fired correctly.
I want to be able to use the requiredfieldvalidator, but I don't want it to create conflict with the button
Why is this happening and How can I solve this?
Thanks...

Answer 1

Use CausesValidation=False in the image button markup:
<asp:ImageButton ID="imgBegin" CausesValidation="False" ImageUrl="~/images/Icon1.jpeg" runat="server" Height="24px" Width="24px" />
You can add that javascript for Button2 in the markup also (instead of OnInit code-behind). Just use OnclientClick attribute in the Button2 mark up