Error message disappears when tabing to next textbox

See more:

ASP.NET

C#3.5

I have a web form that has textboxes and RangeValidator. The validator works and displays but when you tab to another textbox it disappears. Why is that? What setting did I forget?

<asp:RangeValidator ID="RangeValidatorLY1" runat="server" 
                    ControlToValidate="TextBox1" CssClass="style40" 
                    ErrorMessage="20% Difference. Please verify numbers" ForeColor="Red" 
                    Type="Integer" Enabled="True" Display="Dynamic"></asp:RangeValidator>

<asp:TextBox ID="TextBox1" runat="server" Width="180px" AutoPostBack="True" 
                    ontextchanged="TextBox1_TextChanged" CausesValidation="True" 
                    >0</asp:TextBox>

I also have a code behind that formats the value in the textbox.

TextBox1.Text = string.Format("{0:0,0}", double.Parse(TextBox1.Text));

I also have a code behind for the validator.

double txtVal = Convert.ToDouble(TextBoxLY1.Text);
        double minVal = (txtVal * 0.8);
        double maxVal = (txtVal * 1.2);
        RangeValidatorLY1.MinimumValue = minVal.ToString();
        RangeValidatorLY1.MaximumValue = maxVal.ToString();

Here is what is in my textbox text change:

protected void TextBox1_TextChanged(object sender, EventArgs e)
    {
        int w = Convert.ToInt32(TextBox1.Text.Replace(",", ""));
        int v = 0;
        TextBox2.Text = Convert.ToString(w + v);
        RangeValidatorLY1.Validate();
        //TextBoxFTUG.Text = Math.Round(Convert.ToDouble(TextBox1.Text), 2).ToString();
        TextBox1.Text = string.Format("{0:0,0}", double.Parse(TextBox1.Text));
        TextBox3.Focus();

    }