trying to selected value from multiple dropdown lists in loop ??:

Hi,
i have a junction database table called ArtistGenre.
it has ArtistId of type GUID and GenreId of type INT as dual primary keys.
I am trying to insert the selected values of 3 drodown lists into this table.
my code is below but not working - says dropdown is not set to instance object.
any examples to do this is c sharp very appreciated
 

      
 Guid userid = (Guid)Membership.GetUser().ProviderUserKey;

        for (int i = 1; i <= 3; i++)
        {
            DropDownList dropDown = (DropDownList)FindControl("Genredd1, Genredd2, Genredd3" + i.ToString());
 
            if (dropDown.SelectedIndex >= 0)
       ...