previous button shows validations

This is an example of my textbox in my form with a custom validation, I want to disable the validators :

 <asp:textbox id="txtFirstName" runat="server" /></td><td>
        <script language ="javascript">
            function requireFirstName(source, args) {

                if (document.getElementById("<%=txtFirstName.ClientID %>").value =="") {
                    args.IsValid = false;
                }
                else {
                    args.IsValid = true;
                }
            }
      </script>
        <asp:CustomValidator ID="RequiredValidator1" runat="server" 
            ErrorMessage="You must enter your first name." 
             ForeColor="Red" clientvalidationfunction="requireFirstName"
            ></asp:CustomValidator>

This is my previous button:

<asp:Button ID="PreviousButton" runat="server"  
                Text="<-- Back to Instructions" OnClick="btnBack_Click" 
                class="previous"   />
            <script type="javascript">
         开发者_JS百科    document.getElementById("<%=PreviousButton.ClientID%>").disableValidation = true;
            </script>

This will not work and still has validators..help

Try setting CausesValidation to false.

<asp:Button ID="PreviousButton" runat="server" Text="<-- Back to Instructions" OnClick="btnBack_Click" class="previous" CausesValidation="false" />

<asp:Button ID="PreviousButton" runat="server" CausesValidation="false"  
                Text="<-- Back to Instructions" OnClick="btnBack_Click" 
                class="previous" EnableClientScript="false"   />