The key is that you must add the all radiobuttons to your radajaxmanager updated controls. somthing like this

ajaxManager.AjaxSettings.AddAjaxSetting(rbtn1, ddl, pnlLoading);
ajaxManager.AjaxSettings.AddAjaxSetting(rbtn1, rbtn2, null);
ajaxManager.AjaxSettings.AddAjaxSetting(rbtn1, rbtn1, null);
ajaxManager.AjaxSettings.AddAjaxSetting(rbtn2, ddl, pnlLoading);
ajaxManager.AjaxSettings.AddAjaxSetting(rbtn2, rbtn2, null);
ajaxManager.AjaxSettings.AddAjaxSetting(rbtn2, rbtn1, null);

This will solve the problem. because after every postback all the dropdowns must updated.

To load types in other assembly just add the assemblyname via comma at the end of your type:

Type mytype = Type.GetType("Class2, Project2.Library "); 

for nested class you must put plus (+) instead of dot (.):

Type mytype = Type.GetType("Class2+SubClass1, Project2.Library "); 

Add your code in button click add this code (replace your link in the code)

 private void btn_Click(object sender, EventArgs e)
{

.....

 StringBuilder script = new StringBuilder();
script.Append("<script>");
script.AppendFormat("window.open('{0}', '', '');", link);
script.Append("</scri");
script.Append("pt>");
Page.RegisterStartupScript("opennewwindow", script.ToString());

.....

}

public DataView GetTopDataViewRows(DataView source, int count)
{
    DataTable output = source.Table.Clone();
    for (int i = 0; i < count; i++)
    {
        if (i >= source.Count)
            break;
        output.ImportRow(source[i].Row);
    }
    return new DataView(output, source.RowFilter,     source.Sort, source.RowStateFilter);
}