Clicking reset in Views UI causes PDOException Error
Something is trying to serialise a PDO object, which you can't do in PHP (unless you're running &lt; 5.3 and are happy with nasty workarounds). 

Drupal core doesn't do this; The Views module itself doesn't do this; so you'll need to disable custom/contributed modules you have installed one by one until you find the culprit. If/when you do, either fix the module if custom, or report the bug to the module's issue queue on Drupal.org for review.

If you're making use of the PHP filter in that View, remove the PHP code temporarily to see if that's the problem. If it is, consider re-implementing that logic in a more stable manner, i.e. using the hooks from the Views module.