ASP.NET,Gettting Error In The Program

Hi,

please have look into the code and let me know the solution plz. 

string ProID;

try

{

using(SqlConnection conn=new SqlConnection(source))

{

conn.Open();

DataSet ds=new DataSet();

DDLProject.Items.Clear();

SqlCommand cmd=new SqlCommand("SP_ProjectSelect",conn);

cmd.CommandType=CommandType.StoredProcedure;

cmd.Parameters.Add("Name",SqlDbType.NChar,30,"@Name");

cmd.UpdatedRowSource=UpdateRowSource.None;

cmd.Parameters["Name"].Value=DDLProductLine.SelectedItem;

 

SqlDataReader dr=cmd.ExecuteReader(); ------------->>>> Here iam getting Following Error.

 

while(dr.Read())

{ Response.Write(dr["ID"].ToString());

}

 

}

}

catch(System.Exception ex)

{

Response.Write(ex);

}

Error:

System.InvalidCastException: Object must implement IConvertible. at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream) at System.Data.SqlClient.SqlCommand.ExecuteReader() at MIS.UI.ResourceList.DDLProductLine_SelectedIndexChanged(Object sender, EventArgs e) in c:inetpubwwwrootdotnet pgmsmisui
esourcelist.aspx.cs:line 121 

Any suggestion plzz,where went wrong.

Thanks in advance

Regards

Mahesh Reddy