Radiobuttonlist problem

hej.

jag har en radiobuttonlist som jeg fyller med verdier fra en database. og så prøver jeg at ta verdierna fra den och smide denm tilbage til databasen. men jeg får en
Object reference not set to an instance of an object fejl her:
insertCOMPETITOR.Parameters("ANSWER_STRING").value = rblANSWER.SelectedItem.Value

her er min kode:
CMDANSWER = "SELECT ANSWER.ID, ANSWER.ANSWER_TEXT " _
            + "FROM DOIT.COMPETITION, DOIT.QUESTION, DOIT.ANSWER " _
            + "WHERE ANSWER.QUESTION_ID = QUESTION.ID AND QUESTION.COMPETITION_ID = COMPETITION.ID " _
            + "AND COMPETITION.START_DATE < SYSDATE AND COMPETITION.STOP_DATE > SYSDATE ORDER BY ANSWER.QUESTION_ID"
            DS.Tables.Add("COMPETITION")
            DS.Tables.Add("QUESTION")
            DS.Tables.Add("ANSWER")
            DA.SelectCommand = New OracleCommand(CMDANSWER, CN)
            DA.fill(DS, "ANSWER")
           
            CN.close()       

           
            rblANSWER.DataSource = DS.Tables("ANSWER")
            rblANSWER.DataBind()


insertCOMPETITOR.Parameters.Add("ANSWER_STRING", OracleType.VarChar)
insertCOMPETITOR.Parameters("ANSWER_STRING").value = rblANSWER.SelectedItem.Value

insertCOMPETITOR.CommandText = "INSERT INTO DOIT.COMPETITOR (ID,NAME,ADRESS,POSTCODE,TOWN,TELEPHONE,EMAIL,ANSWER_STRING,PLACEMENT,NUMOFRIGHTS,COMPETE_DATE,NEWSLETTER,COMPETITION_ID)" _
            + " VALUES (COMPETITOR_SEQ.nextval, :NAME, :ADRESS, :POSTCODE, :TOWN, :TELEPHONE, :EMAIL, :ANSWER_STRING, :PLACEMENT, :NUMOFRIGHTS, to_date(:COMPETE_DATE, 'MM-DD-YYYY'), :NEWSLETTER, :COMPETITION_ID)"
            insertCOMPETITOR.ExecuteNonQuery()