how to pass dropdownlist value which is connected to an sqldatasource to another page?

 hi everyone,
im having a problem like i could not pass a value of a dropdownlist connected to an sqldatasource.
is it the same with passing a value from a textbox to another page?
i did it like this
 
 
 Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
subjectDDL.SelectedValue.ToString()
 
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click

 Dim targetURL As String

        targetURL = "save2.aspx?"
   targetURL &= "subject= " & subjectDDL.SelectedValue.ToString()
        Response.Redirect(targetURL)
 
at save2.aspx
 
 instructor.Text = Request.QueryString("subject").ToString()
 
i got this error