ASP.NET MVC3 & ExtJS4 Errors

/// <summary>
/// Used for AJAX error handling.
/// Causes unhandled exceptions to become JSON messages such as:
/// {ExceptionType:...,Message:...,StackTrace...}
/// Request set to HTTP error code 500.
/// </summary>
public class CustomAjaxErrorHandler : FilterAttribute, IExceptionFilter
{
	public void OnException(ExceptionContext filterContext)
	{
		Exception e = filterContext.Exception;
		// Prevent text dump of exception
		filterContext.ExceptionHandled = true;
		// 500 HTTP status
		filterContext.RequestContext.HttpContext.Response.StatusCode =
			(int)HttpStatusCode.InternalServerError;
		filterContext.Result = new JsonResult
		{
			Data = new 
			{ // Returned JSON
				ExceptionType = e.GetType().ToString(),
				Message = e.Message,
				StackTrace = e.ToString()
			},
			JsonRequestBehavior = JsonRequestBehavior.AllowGet
		};
	}
}

[HttpPost]
[CustomAjaxErrorHandler]
public ContentResult Search( string query )
{
	throw new Exception("Test error message!");
	...
}

// Intercepting from XML store
Ext.create('Ext.data.Store',{
	model: 'MY.model.SearchResult',
	proxy: Ext.create('MY.proxy.MSAjaxProxy', {
		url: '/User/Search',
		reader: { type: 'xml', root: 'matches', record: 'match' },
		listeners: {
			exception: function( thisProxy, response, operation, options ) {
				handleAjaxError(response);
			}
		} // eo listeners
	}) // eo proxy
}) // eo store
 
// Intercepting from simple Ajax call
Ext.Ajax.request({
	...
	failure: function(response) { 
		handleAjaxError(response);
	},
	success: function(response) { ... }
}); // eo Ajax
 
// Custom error handler window
handleAjaxError = function ( ajaxResponse ) {
	var responseData = Ext.JSON.decode(ajaxResponse.responseText),
		win = null,
		windowConfig = null;
 
	if (!responseData) // request timed out?
	{
		responseData = {
			ExceptionType: 'Timeout',
			Message: 'It appears the request timed out, please try again!' 
		};
	}
 
	// Window to show
	windowConfig = {
		title: 'Error: ' + Ext.htmlEncode(responseData.ExceptionType),
		layout: 'anchor',
		defaults: { anchor: '100%' },
		modal: true,
		resizable: false,
		width: 400,
		items: 
		[
			{ 
				xtype: 'container'
				, autoScroll: true
				, html: '<img style="float: left; padding: 5px;" src="../extjs/resources/themes/images/gray/shared/icon-error.gif">'
					+ Ext.htmlEncode(responseData.Message)
			}
		], // eo items
		buttons:
		[
			{ text: 'OK', handler: function() { win.destroy(); } }
		], // eo buttons
		listeners: {
			afterrender: { // make sure layout sized properly
				single: true,
				buffer: 10,
				fn: function() { return; win.doLayout(); }
			} // eo afterrender
		} // eo listeners
	};
 
	// Stack trace panel on the bottom?
	if ( responseData.StackTrace )
	{
		windowConfig.items.push({
			xtype: 'panel',
			title: 'Stack Trace',
			collapsible: true,
			collapsed: true,
			titleCollapse: true,
			layout: 'fit',
			listeners: {
				collapse: function() { win.doLayout(); },
				expand: function() { win.doLayout(); } 
			},
			items: {
				xtype: 'textarea',
				readOnly: true,
				height: 150,
				value: responseData.StackTrace
			}
		});
	}
 
	win = Ext.create('Ext.window.Window', windowConfig);
	win.show();
}