jQuery .blur() does not fire nor does .focusout()?

jQuery .blur() does not fire nor does .focusout()?

New to jquery so it is possible I've missed a vital element somewhere
along the lines. I've been digging for the past couple of hours and have
tried several solutions but nothing I've tried solves the delima. All I'm
trying to do is execute some code once "textboxUsername" looses focus. In
straight javascript I used to do this by adding an onblur() event to the
specific input element and call a function. Any advice appreciated...
HTML:
<div>
<div class="heading">
<span class="inside_heading">Register</span>
</div>
<div class="content_under_heading">
<div class="rounded_div">
<ul class="ulRegister">
<li class="descLabel">
Username:
</li>
<li class="inputInfo">
<input type="text" id="textboxUsername"/>
</li>
<li class="successCheck" id="usernameSuccessCheck">
<img id="usernameCheckImage"
src="templates/images/check.png" class="noShow"/>
<img id="usernameXImage" src="templates/images/check.png"
class="noShow"/>
</li>
</ul>
<label id="labelUsernameExists" class="registerIssue"></label>
</div>
</div>
</div>
JavaScript
$(document).ready(function(){
//textboxUsername blur event
$("#textboxUsername").blur(function(){
var possibleUsername = $("#textboxUsername").val();
if(possibleUsername.length != 0){
if(possibleUsername.length < 6){
//display message
var message = "Usernames must be at least 6 characters";
$("#labelUsernameExists").text(message);
} else{
//ajax
}
}
});
});