A circular reference was detected while serializing an object of type 'SubSonic.Schema .DatabaseColumn'.

It seems that there are circular references in your object hierarchy which is not supported by the JSON serializer. Do you need all the columns? You could pick up only the properties you need in the view:

return Json(new 
{  
    PropertyINeed1 = data.PropertyINeed1,
    PropertyINeed2 = data.PropertyINeed2
});

This will make your JSON object lighter and easier to understand. If you have many properties, AutoMapper could be used to automatically map between DTO objects and View objects.

I had the same problem and solved by using Newtonsoft.Json;

var list = JsonConvert.SerializeObject(model,
    Formatting.None,
    new JsonSerializerSettings() {
        ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
});

return Content(list, "application/json");

This actually happens because the complex objects are what makes the resulting json object fails. And it fails because when the object is mapped it maps the children, which maps their parents, making a circular reference to occur. Json would take infinite time to serialize it, so it prevents the problem with the exception.

Entity Framework mapping also produces the same behavior, and the solution is to discard all unwanted properties.

Just expliciting the final answer, the whole code would be:

public JsonResult getJson()
{
    DataContext db = new DataContext ();

    return this.Json(
           new {
                Result = (from obj in db.Things select new {Id = obj.Id, Name = obj.Name})
               }
           , JsonRequestBehavior.AllowGet
           );
}

It could also be the following in case you don't want the objects inside a Result property:

public JsonResult getJson()
{
    DataContext db = new DataContext ();

    return this.Json(
           (from obj in db.Things select new {Id = obj.Id, Name = obj.Name})
           , JsonRequestBehavior.AllowGet
           );
}