Validators postback unwanted
<p>I have multiple validators in my web page (compare, required, custom). When I click submit button, the page postsback. However I have given same validation group to all the fields. What is wrong?</p>

<pre><code> &lt;div class="innerUserName" style="margin-top: 0px;"&gt;
                                &lt;asp:TextBox ID="txtUserName" runat="server" ClientIDMode="Static" 
                                    MaxLength="20" Style="margin-left: 28px;" Width="230" CausesValidation="True"&gt;&lt;/asp:TextBox&gt;

                            &lt;/div&gt;

 &lt;asp:HiddenField ID="hdnField" runat="server" ClientIDMode="Static" /&gt;
                            &lt;div id="divUserNameAvailability"&gt;
                            &lt;/div&gt;
                            &lt;asp:RequiredFieldValidator ID="reqval_UName" runat="server" ControlToValidate="txtUserName"
                                CssClass="validation" Display="Dynamic" ErrorMessage="Please Provide User Name"
                                SetFocusOnError="True" ValidationGroup="SignUp"&gt;&lt;/asp:RequiredFieldValidator&gt;
                                &lt;%--User Name Not Available--%&gt;
                            &lt;asp:CustomValidator ID="cusval_UName" runat="server" ErrorMessage="" ClientIDMode="Static"
                                ClientValidationFunction="ValidateUsername" ControlToValidate="txtUserName" CssClass="validation"
                                Display="Dynamic" SetFocusOnError="True" ValidationGroup="SignUp"&gt;&lt;/asp:CustomValidator&gt;


&lt;div class="innerPwd" style="margin-top: 0px;"&gt;
                                &lt;asp:TextBox ID="txtPassword" runat="server" TextMode="Password" 
                                    Style="margin-left: 28px;" Width="230" CausesValidation="True"&gt;&lt;/asp:TextBox&gt;
&lt;/div&gt;

 &lt;span&gt;
                            &lt;asp:RequiredFieldValidator ID="reqval_Pwd" runat="server" ControlToValidate="txtPassword"
                                SetFocusOnError="true" CssClass="validation" Display="Dynamic" ErrorMessage="Please Provide Password"
                                ValidationGroup="SignUp" /&gt;
                            &lt;asp:RegularExpressionValidator ID="regexPassword" runat="server" ControlToValidate="txtPassword"
                                SetFocusOnError="true" Display="Dynamic" ErrorMessage="Please Provide Valid Password"
                                ValidationExpression="^(?=.*[0-9]+.*)(?=.*[a-zA-Z]+.*)[0-9a-zA-Z]{6,20}$" ValidationGroup="SignUp"
                                CssClass="validation"&gt;&lt;/asp:RegularExpressionValidator&gt;&lt;/span&gt;
                        &lt;div&gt;



&lt;asp:Button ID="btnSignUp" runat="server" Text="Create Account" Style="border: 0px;
                                    background-color: #396fd1; font-weight: bold; height: 29px; font-size: 12px;
                                    color: #fff3dd;" ValidationGroup="SignUp" /&gt;
</code></pre>

<p>function:</p>

<pre><code>function ValidateUsername(sender, args) {
            var div = document.getElementById("divUserNameAvailability");
            var img = document.getElementById("imgUserNameAvailability");

            if (div.style.display == "none") {
                CallMe("txtUserName");
            }

            if (div.style.display == "inline") {
                var imgFileName = getName(img.src);
                if (imgFileName == "wrong")
                    args.IsValid = false;
                else
                    args.IsValid = true;
            }
        }
</code></pre>
