I am using Grid.MVC available at http://gridmvc.azurewebsites.net/, which provides functionality for displaying the data in grid nicely, where filtering, sorting, paging is
You need to look more closely at AJAX validation and client side validation. Basically what's happening is the partial view you are loading which contains your edit form does not have validation bound to it since it was loaded after the initial page load. You can try adding this to your page (JQuery):
$.validator.unobtrusive.parse('#formId');
where formId is the ID of your HTML form. You also need to use Ajax.BeginForm helper instead of Html helper you're using.
Beyond that take a look at post:
ASP.NET MVC client validation with partial views and Ajax