I have a frustrating problem with the subgrid. When clicking the “+” to enlarge a subgrid, Firebug shows that data is being returned, but the subgrid expands empty. My subgrid model is based on a similar subgrid that works correctly. For debguing, I've reduced the subgrid to a single column (still no luck). Please advise.

Here is the code:

jQuery(document).ready(function(){