TextChanged is not firing in update panel.

Hi all,

I have a text box in my update panel.

I need to do somtning on the TextChanged event of the textbox but it is not firing. Why ?

below is my cs code.

protected void txtSanctionAmountContract_TextChanged(object sender, EventArgs e)
    {
        double San_Contract_Amt = Convert.ToDouble(txtSanctionAmountContract.Text);
        double San_DPR_Amt = Convert.ToDouble(txtSanctionAmountDPR.Text);
        if (San_DPR_Amt < San_Contract_Amt)
        {
            WebMsgBox.Show("Contract amount should not be greater than DPR amount.");
        }

    }

Thanks