C#

if(string.IsNullOrEmpty(TextBox1.Text)){}

private void textBox1_TextChanged(object sender, EventArgs e)
{
    if (textBox1.Text.Trim() != "")
    {
        decimal j;
        if (!decimal.TryParse(textBox1.Text, out j))
        {
            MessageBox.Show("Not allowed!!!");
            textBox1.Text = "";
        }
    }
}

void textBox1_TextChanged(object sender, EventArgs e)
        {
            if (textBox1.Text.Trim() != "")
            {
                decimal j;
                if (!decimal.TryParse(textBox1.Text, out j))
                {
                    MessageBox.Show("Not allowed!!!");
                    textBox1.Text = "";
                }
            }
        } 

• Hook TextChanged to make sure that the value can never be invalid, e.g. if you try to paste into it, set the text programatically (e.g. through data binding) or any other way of putting text in there. Note that 'valid content' isn't necessarily a valid number, because you need to allow intermediate input that someone will type while entering a number. For example '', '-', '3.', '6E' (if supporting exponential notation) and the like should be allowed. You can find or write a regex for this part.
• Hook the keyboard input events (KeyPress should be enough) to reject any characters that can never be allowed, e.g. anything but numbers, or a minus sign in an empty field, or a dot. This prevents the TextChanged handler from firing, wiping the invalid character but resetting the caret.
• Have a numeric Value property that you can read and write in code.

Actually sir the thing is that event will also be called when code exit out of backup....so i think thats not an issue....The main thing is, the line 

Process process=Process.Start(psi);

is not executing....and after this line i m getting error.....

try
        {
            
            //OleDbCommand oleDbCmd = new OleDbCommand("Select * From [Sheet1]", oleDbCon);            
            //oleDbDa.SelectCommand = oleDbCmd;            
            oleDbDa.Fill(ds,"ServerName");
            DataTable dt = ds.Tables["ServerName"];
            //string str1stValue = ds.Tables[0].Rows[0][0].ToString();
            foreach(DataRow dr in dt.Rows)
            {
                foreach (DataColumn dc in dt.Columns)
                    strServerName.Append(dr[dc].ToString()).Append("\",\"");
                    //strServerName.AppendFormat("\",\"", dr[dc].ToString());
            }
           //strFinalList = strFinalList.AppendFormat("\",\"", strServerName);
            Response.Write(strServerName);
        }