Cannot implicitly convert type 'string' to 'int'

The error is generated because the key for getting data from your deserialized object is expected to be int and not string. So the solution could be :

void wc_DownloadStringCompleted1(object sender, DownloadStringCompletedEventArgs e1)
        {
            var serializer1 = new JavaScriptSerializer();
            serializer1.RegisterConverters(new[] { new DynamicJsonConverter() });
            dynamic obj = serializer1.Deserialize(e1.Result, typeof(object)); //You have to inspect the value of obj after this line in Debug!
            int dd =Int32.Parse(obj[0]); //Or other numeric value!
            int fn1 =Int32.Parse(obj[1]);//Or other numeric value!
            lblitemname.Text = fn1.ToString(); //A string is expected!
        }

You should try the above code, but better is to inspect in Debug the obj object to see its properties and keys.

the error clearly shows message that you can not convert string to int format.
you trying the same in 6th line.

try to change:-

dynamic fn1 =Int32.Parse(obj["Formatted Name"]);

to

dynamic fn1 =obj["Formatted Name"].ToString();

Int32.Parse can't convert the value of the obj["Formatted Name"] to int, probably there isn't a correct int format value in it.

If you would like to add as a text the value for your label, try this:

if (obj["Formatted Name"] != null)
{
    lblitemname.Text = obj["Formatted Name"].ToString();
}

Try this:

lblitemname.Text = fn1.ToString();

Can you add null check before type casting. It might have null value.

This is the solution of my problem.

void wc_DownloadStringCompleted1(object sender, DownloadStringCompletedEventArgs e)
        {
            try
            {
                var serializer1 = new JavaScriptSerializer();
                serializer1.RegisterConverters(new[] { new DynamicJsonConverter() });

                dynamic obj = serializer1.Deserialize(e.Result, typeof(object));
                     
			dynamic obj7 = obj[7]; 
                        dynamic fn7 = obj7["Formatted Name"]; 
                        lblitemname.Text = fn7;
           }
            catch (Exception ex)
            {
            }
        }

You can rather use int.TryParse so that id would confirm first that the objects like obj["HierarchyPosition"] is integer value or not