Same drupal webform is showing error messages in two different way, on different palces in the same website
Try to use Webform Validation module. I hope through this you can solve your issue.


  This module adds an extra tab to each webform node, allowing you to
  specify validation rules for your webform components. You can create
  one or more of the predefined validation rules, and select which
  webform component(s) should be validated against those. By using the
  hooks provided by this module, you can also define your own validation
  rules in your own modules.