The ParentError.aspx page described earlier tries to close the popup browser window after passing the error to the parent page. If the javascript just calls window.close(), Internet Explorer prompts the user if they want to allow the page to close. With the following code, the window will close without a prompt and it works in both IE and Firefox:

// close the window without a prompt in both IE and Firefox
window.open('', '_self');
window.close();