Broadly there are 2 type of errors:
1) Unexpected or uncatched errors like 404 or 500 server errors.
dataModel.error callback can be implentend to handle or troubleshoot these kind of errors:
http://paramquery.com/pro/api#option-dataModel-errorIf direct Ajax calls are made with jQuery, then $.ajax( { error: function(){} } can be used to handle/ troubleshoot the errors.
http://api.jquery.com/jquery.ajax/2) catched errors whereby more user friendly messages are returned by the server.
In this case, dataModel.getData( response ) callback can be used to handle/display the error response to user depending upon the format of the error message.
and success callback can be used in case of direct call through jQuery ajax method.