Drupal: Validate File Extension?

[cool1]

I'm trying to validate that an uploaded file really does have the \[code\].csv\[/code\] extension. This code isn't working, however:\[code\]function upload_validate($form, &$form_state) { // code that does work ... else { $file = file_save_upload('upload'); $errors = file_validate_extensions($file, 'csv'); if (! empty($errors)) { form_set_error('', $errors[0]); } else { $_SESSION[FILE_KEY] = serialize($file); } }}\[/code\]What am I doing wrong?