'JQuery' is undefined

Question

I am working on a ASP.net project created with local file system settings. I am using MVC and Jquery. Jquery is working fine when I run the application in debug mode i.e. in

Answer 1

I got the message by having a mismatch between the version of JavaScript in the page and the version in the project.

On the page: <script src="@Url.Content("~/Scripts/jquery-1.4.4.min.js")" type="text/javascript">

Actual version in the project: jquery-1.4.1.min.js

Diagnosed by using Firebug, and setting it show all errors, as described in the accepted answer.