Question

This code is copied from another file and it works in that file, I have checked the variable and form id and i am sure that the name is consistent with the js code. The textbox in genFrom is also validate working, only the checkbox is not working.

<script src="http://code.jquery.com/jquery-1.6.1.min.js"></script>
<script src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.9/jquery.validate.min.js"></script>
<script>
$(document).ready(function(){
    $("#genForm").validate();
    $("#genForm").validate( {
        rules: {
            agree: {
                required: true
            }
        }
    })
});
</script>

<form id="genForm"  method="post" action="verify.php">
<div class="container">
    <div class="hero-unit">
        <h1>Subscribe for final</h1>
    </div>
    <div class="clearfix">
        <label>Email</label>
        <div class="input">
            <input name="Email" type="text" class='required'>
        </div>
    </div>
    <br>
    <br>
    <div class="clearfix">
    <label>Agreements:</label>
        <div class="input"> 
        <ul class="inputs-list">
            <li>                                      
            I accept the terms and conditions.
            <!-- Check box is here, not working -->
            <input type="checkbox" name="agree" value="1">
            </li>
        </ul>
        </div> 
    </div> 
    <br>
    <input class="btn primary" type="submit" value="Submit">
</form>

Answer 1

For some reason, you’re calling validate() twice on the same form, you only need one:

// $("#genForm").validate(); No need for this

$("#genForm").validate( {
  rules: {
      agree: {
          required: true
      }
   }
});

Demo: http://jsfiddle.net/8MV5F/

Calling validate() with no params does have some (configurable) default behavior, one of which is attaching the required rule to elements with class='required', which is why the email field was working. You can also use the required attribute for that, and in addition you can use type="email" to validate as an email address without specifying it in your rules.

Here’s a simple example: http://jsfiddle.net/8MV5F/2/

<form id="genForm"  method="post" action="verify.php">
    <label>Email:<input name="Email" type="email" required></label>          
    <label>I accept the terms and conditions.
    <input type="checkbox" name="agree" value="1" required></label>
    <input class="btn primary" type="submit" value="Submit">
</form>

$("#genForm").validate();

This has the advantage of falling back to native browser validation if supported, in case javascript is disabled, or even just broken.