single textbox with different validation

Question

<div class="search-container">
<label>
<br />
<br />
<br />
Sort By</label>

<asp:TextBox ID="txtsearch" runat="server" placeholder="Search by Product Name/Brand Name/Product Description...." Width="460px"></asp:TextBox>

Price Min : <asp:TextBox ID="txtminprice" ValidationGroup="productvalidate" runat="server"></asp:TextBox>
Max : <asp:TextBox ID="txtmaxprice" ValidationGroup="productvalidate" runat="server"></asp:TextBox>
<asp:CustomValidator ID="CustomValidator1" runat="server" Display="Dynamic" ErrorMessage="CustomValidator" ForeColor="Red" ValidationGroup="productvalidate" OnServerValidate="CustomValidator_ServerValidate"></asp:CustomValidator>
<asp:CompareValidator ID="CompareValidator1" ForeColor="Red" runat="server" Display="Dynamic" ControlToValidate="txtmaxprice" ValidationGroup="productvalidate" ControlToCompare="txtminprice" operator="GreaterThan" type="Double" ErrorMessage="max price must be grater than"></asp:CompareValidator>
<br /> <br />
Date From : <asp:TextBox ID="txtdatefrom" autocomplete="off" runat="server"></asp:TextBox>
<cc1:CalendarExtender ID="CalendarExtender1" Format="yyyy-M-dd" TargetControlID="txtdatefrom" runat="server"></cc1:CalendarExtender>
Date To : <asp:TextBox ID="txtdateto" autocomplete="off" runat="server"></asp:TextBox>
<cc1:CalendarExtender ID="CalendarExtender2" TargetControlID="txtdateto" Format="yyyy-M-dd" runat="server"></cc1:CalendarExtender>
<asp:CustomValidator ID="CustomValidator2" runat="server" Display="Dynamic" ErrorMessage="CustomValidator" ForeColor="Red" ValidationGroup="productvalidate" OnServerValidate="CustomValidator_ServerValidate1"></asp:CustomValidator>
<asp:CompareValidator ID="CompareValidator2" runat="server" ControlToValidate="txtdateto" Display="Dynamic" ValidationGroup="productvalidate" ForeColor="Red" ControlToCompare="txtdatefrom" operator="GreaterThan" type="Date" ErrorMessage="toDate must be grater than"></asp:CompareValidator>
<asp:CustomValidator ID="CustomValidator3" runat="server" ErrorMessage="CustomValidator" ForeColor="Red" Display="Dynamic" ValidationGroup="productvalidate" OnServerValidate="CustomValidator_ServerValidate2"></asp:CustomValidator>
<asp:ImageButton ID="btnsearchs" style="float:right" OnClick="btnsearchs_Click" Height="60px" ValidationGroup="productvalidate" runat="server" ImageUrl="~/Images/btnsearch.png" />
</div>

public void CustomValidator_ServerValidate(object source, System.Web.UI.WebControls.ServerValidateEventArgs args)
{
args.IsValid = true;
if ((txtminprice.Text != "" && txtmaxprice.Text == "") || (txtminprice.Text == "" && txtmaxprice.Text != ""))
{
CustomValidator1.ErrorMessage = "Enter value in at Both text Box";
args.IsValid = false;
}
}
public void CustomValidator_ServerValidate1(object source, System.Web.UI.WebControls.ServerValidateEventArgs args)
{
args.IsValid = true;
if ((txtdatefrom.Text != "" && txtdateto.Text == "") || (txtdatefrom.Text == "" && txtdateto.Text != ""))
{
CustomValidator2.ErrorMessage = "Enter value in at Both text Box";
args.IsValid = false;
}
}
public void CustomValidator_ServerValidate2(object source, System.Web.UI.WebControls.ServerValidateEventArgs args)
{
args.IsValid = true;
if ((txtdatefrom.Text == "" && txtdateto.Text == "") && (txtminprice.Text == "" && txtmaxprice.Text == "") && (txtsearch.Text==""))
{
CustomValidator3.ErrorMessage = "Select atleast one selection";
args.IsValid = false;
}
}

this is my code ,the problem is after showing error message ,reenter correct input but it always shown, after button click is working fine, please tell solution of this problem