jQuery Grid Plugin - jqGrid

I'm trying to get the jqGrid plugin up and running. But, i get this error from the firebug console:

jQuery("#schedule-table").jqGrid is not a function
(?)()()
handleError()()jquery.js (line 28)
handleError()()jquery.js (line 28)
nodeName()([function(), function()], function(), undefined)jquery.js (line 22)
handleError()()jquery.js (line 28)

At first i thought i probably hadn't properly loaded to the jquery.jqGrid.js file, but it's definitely being loaded - i put an alert in the "jqGridInclude()" function and it fires when the page starts loading.

I'm copying the 'getting started' example from this page - http://trirand.com/jqgrid/jqgrid.html

I seen other reports of this (one on this forum, one in russian!) and the suggestion was to edit this line in the main jqgrid file:

var pathtojsfiles = "js/"; // need to be ajusted

If that's the case, i have no idea what to adjust it to:  the files are all in their default locations.  I'm using it in a rails app, so i have a public/javascripts folder to contain all my js files.  Inside that is a folder called jqGrid, which has the main file, jquery.jqGrid.js, and a 'js' folder with the various files used by jqGrid.  So, the path variable above looks ok.

Can anyone help?
thanks
max