[jQuery] Problem with $(document) and actually with every $(...) call

[PCPbSlack]

First of all, thanks for this wonderful library.

Then here is my problem. I updated my jQuery library in my
application  with the latest version (1.1.4) and I have the following
issue:

jQuery(document).ready(function() {
        jQuery("#user_name").focus();
});

works just fine, but my old:

$(document).ready(function() {
        $("#user_name").focus();
});

The error I am getting is: $ is not a function.

I mention that using jQuery version 1.1.3.1, the above issue is not
happening.

What is going on?

Thanks all.