Data Controls :: Trying To Download File From Database

I get this error when trying to download the file

Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.Modules.ID_LIT.View.GetData(SqlCommand cmd) at DotNetNuke.Modules.ID_LIT.View.Button4_Click(Object sender, EventArgs e) at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---

I am using this example from your site:

[URL]

here is my code:

Public Function GetData(ByVal cmd As SqlCommand) As DataTable
Dim dt As New DataTable
Dim strConnString As String = System.Configuration.ConfigurationManager.ConnectionStrings("mystring").ConnectionString
Dim con As New SqlConnection(strConnString)
Dim sda As New SqlDataAdapter
cmd.CommandType = CommandType.Text
cmd.Connection = con

[CODE]...