Can somebody clue me into what this error is about? 

[Exception... "Cannot convert WrappedNative to function" nsresult: "0x8057000d (NS_ERROR_XPC_CANT_CONVERT_WN_TO_FUN)" location: "JS frame :: http://localhost:8080/ads/js/dojo-1.1.1/dojo/dojo.js.uncompressed.js :: anonymous :: line 486" data: no] message=Cannot convert WrappedNative to function

Here’s the code that’s generating it.

var towData2 = {

            identifier:'towId',

            items:[

                  { towId:'1', towWarning:'', towError:'' }

            ]

      };

var towStore = new dojo.data.ItemFileReadStore({data: towData2});