Hello,

If you could try the below example I'm receiving an unexpected response from the create action.

ExampleController.cs:
    public class ExampleController : System.Web.Mvc.Controller
    {
        public ActionResult Index()
        {
            return View();
        }

        public ActionResult Create()
        {
            var result = new AjaxStoreResult
            {
                ResponseFormat = StoreResponseFormat.Save
            };

            result.SaveResponse.Success = true;

            return result;
        }

        public ActionResult Update()
        {
            var result = new AjaxStoreResult
            {
                ResponseFormat = StoreResponseFormat.Save
            };

            result.SaveResponse.Success = true;

            return result;
        }

        public ActionResult GetData()
        {
            IList result = new List<object>();

            result.Add(new
            {
                Id = 1,
                Name = "Timothy"
            } );

            result.Add(new
            {
                Id = 2,
                Name = "Geoffrey"
            } );

            return new AjaxStoreResult
            {
                ResponseFormat = StoreResponseFormat.Load,
                Data = result,
                Total = result.Count
            };
        }
    }
Index.aspx:
<%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Example</title>
</head>
<body>
    <ext:ResourceManager ID="ResourceManager1" runat="server" ScriptMode="Debug" />
    <ext:GridPanel ID="GridPanel1" runat="server"
        AutoExpandColumn="Name"
        Height="250"
        Layout="fit">
        <Store>
            <ext:Store ID="Store1" runat="server"
                AutoLoad="true"
                RemotePaging="true"
                RemoteSort="true"
                Restful="true">
                <Proxy>
                    <ext:HttpProxy Json="true">
                        <RestAPI
                            Create="/Example/Create"
                            Destroy="/Example/Delete"
                            Read="/Example/GetData"
                            Update="/Example/Update" />
                    </ext:HttpProxy>
                </Proxy>
                <Listeners>
                    <Exception Handler="
                        Ext.net.Notification.show({
                            iconCls    : 'icon-exclamation', 
                            html       : e &amp;&amp; e.message ? e.message : response.message || response.statusText, 
                            title      : 'EXCEPTION', 
                            hideDelay  : 5000
                        });" />
                    <Save Handler=" Ext.net.Notification.show({
                            iconCls    : 'icon-information', 
                            html       : arg.message, 
                            title      : 'Success', 
                            hideDelay  : 5000
                        });" />
                </Listeners>
                <Reader>
                    <ext:JsonReader IDProperty="Id" Root="data" SuccessProperty="success">
                        <Fields>
                            <ext:RecordField Name="Id" />
                            <ext:RecordField Name="Name" SortDir="ASC" />
                        </Fields>
                    </ext:JsonReader>
                </Reader>
            </ext:Store>
        </Store>
        <BottomBar>
            <ext:Toolbar runat="server">
                <Items>
                    <ext:Button runat="server" Text="Add vladimir">
                        <Listeners>
                            <Click Handler="#{GridPanel1}.insertRecord(0, { Name : 'vladimir' } ); #{GridPanel1}.save();" />
                        </Listeners>
                    </ext:Button>
                </Items>
            </ext:Toolbar>
        </BottomBar>
        <ColumnModel>
            <Columns>
                <ext:Column ColumnID="Name" DataIndex="Name" Header="Name">
                    <Editor>
                        <ext:TextField runat="server" />
                    </Editor>
                </ext:Column>
            </Columns>
        </ColumnModel>
        <Plugins>
            <ext:RowEditor runat="server" ClicksToEdit="2" SaveText="Update">
                <Listeners>
                    <AfterEdit Handler="#{GridPanel1}.save();" />
                </Listeners>
            </ext:RowEditor>
        </Plugins>
    </ext:GridPanel>
</body>
</html>
Replication steps:

1. Load page
2. Click Add vladimir
3. Notice it throws an exception in the bottom right corner?

Update works with the same method. Can you help? Would really like to get this working soon!

Cheers,
Timothy