TypeError: $(…).modal is not a function with bootstrap Modal

I have a bootstrap 2.32 modal which I am trying to dynamically insert into the HTML of another view. I’m working with Codeigniter 2.1. Following Dynamically inserting a bootstrap modal partial view into a view, I have:

<div id="modal_target"></div>

as the target div for insertion. I have a button in my view that looks like:

     <a href="#message" class="btn btn-large btn-info" data-action="Message" data-toggle="tab">Message</a>

My JS has:

$.ajax({
    type    : 'POST', 
    url     : "AjaxUpdate/get_modal",
    cache   : false,
    success : function(data){ 
       if(data){
            $('#modal_target').html(data);

            //This shows the modal
            $('#form-content').modal();
       }
    }
});

The button of the main view is:

<div id="thanks"><p><a data-toggle="modal" href="#form-content" class="btn btn-primary btn-large">Modal powers, activate!</a></p></div>

Here is what I’d like to store separately as a partial view:

<div id="form-content" class="modal hide fade in" style="display: none;">
    <div class="modal-header">
        <a class="close" data-dismiss="modal">×</a>
        <h3>Send me a message</h3>
    </div>
    <div class="modal-body">
        <form class="contact" name="contact">
             <fieldset>

               <!-- Form Name -->

            <legend>modalForm</legend>

            <!-- Text input-->
            <div class="control-group">
              <label class="control-label" for="user">User</label>
              <div class="controls">
                <input id="user" name="user" type="text" placeholder="User" class="input-xlarge" required="">
                <p class="help-block">help</p>
              </div>
            </div>

            <!-- Text input-->
            <div class="control-group">
              <label class="control-label" for="old">Old password</label>
              <div class="controls">
                <input id="old" name="old" type="text" placeholder="placeholder" class="input-xlarge">
                <p class="help-block">help</p>
              </div>
            </div>

            <!-- Text input-->
            <div class="control-group">
              <label class="control-label" for="new">New password</label>
              <div class="controls">
                <input id="new" name="new" type="text" placeholder="placeholder" class="input-xlarge">
                <p class="help-block">help</p>
              </div>
            </div>

            <!-- Text input-->
            <div class="control-group">
              <label class="control-label" for="repeat">Repeat new password</label>
              <div class="controls">
                <input id="repeat" name="repeat" type="text" placeholder="placeholder" class="input-xlarge">
                <p class="help-block">help</p>
              </div>
            </div>



                </fieldset>
        </form>
    </div>


    <div class="modal-footer">
        <input class="btn btn-success" type="submit" value="Send!" id="submit">
        <a href="#" class="btn" data-dismiss="modal">Nah.</a>
    </div>
</div>

When I click the button, the modal is inserted correctly, but I get the following error:

TypeError: $(...).modal is not a function 

How can I fix this?