title: Textbox Locks up
body: <p>I'm using Visual Studio 2015 - ASP DOTNET C# and WebForms
  I've written a program and part of it requires the user to input a number via a textbox, when the user tabs out the event fires successfully and retrieves the record populating all relevant fields on the form.</p>
  
  <p>Sometimes the user can input another number and it fires, on occasion the textbox locks up as if the read only is true, it won't allow you to delete the text, input further text etc, you have to click a random button on the page which then clears the issue. I'm pretty stumped as to why it's doing this.</p>
  
  <pre><code>protected void txtAsset_TextChanged(object sender, EventArgs e)
  {
      //Validate text input
      lblSuccessful.Text = string.Empty;
      txtAsset.Focus();
      string input = txtAsset.Text;
           if (!Regex.IsMatch(input, @"^[0-9]\d*"))
           {
                lblSuccessful.CssClass = "ErrorMessage";
                lblSuccessful.Text = "You have input invalid criteria";
                txtAsset.Text = string.Empty;
                txtAsset.Focus();
           }
           else
           {
                Execute Retrieval of record code
           }
  }
  </code></pre>
  
  <p>Many thanks for your help</p>