Fatal error in e-Newsletter if Double Opt In option is checked

Hi, I am receiving this error:
Fatal error: Cannot redeclare class phpmailerException in /sites/ceiba/wp-content/plugins/e-newsletter/email-newsletter-files/phpmailer/class.phpmailer.php on line 2319

If the option of Double Opt in option is checked and I try to add an address using the widget. I can send Newsletters and test messages but that confirmation message gives an error. I would appreciate any suggestion.