Thank you for reporting this problem. It appears to be a bug.
to fix the problem, update that line to:
$WA_MailObject->ReplyTo = "". (ValidatedField("contactme","Contact_me_group_Email")) . "";
I will make sure this bug is logged and fixed. Thank you for bringing it to our attention... but actually that value doesn't make sense. The "ValidatedField" should actually only be used to repopulate a form after failed validation. You should be using the form field value itself when binding in other server behaviors.... so really it should probably be:
$WA_MailObject->ReplyTo = "". (isset($_POST["Contact_me_group_Email"])?$_POST["Contact_me_group_Email"]:"") . "";